blob: 3dca7227a91c3876126cb6ca268c09c41ecbfdf4 [file] [log] [blame]
What's New In Python 3.3
.. Rules for maintenance:
* Anyone can add text to this document. Do not spend very much time
on the wording of your changes, because your text will probably
get rewritten to some degree.
* The maintainer will go through Misc/NEWS periodically and add
changes; it's therefore more important to add your changes to
Misc/NEWS than to this file.
* This is not a complete list of every single change; completeness
is the purpose of Misc/NEWS. Some changes I consider too small
or esoteric to include. If such a change is added to the text,
I'll just remove it. (This is another reason you shouldn't spend
too much time on writing your addition.)
* If you want to draw your new text to the attention of the
maintainer, add 'XXX' to the beginning of the paragraph or
* It's OK to just add a fragmentary note about a change. For
example: "XXX Describe the transmogrify() function added to the
socket module." The maintainer will research the change and
write the necessary text.
* You can comment out your additions if you like, but it's not
necessary (especially when a final release is some months away).
* Credit the author of a patch or bugfix. Just the name is
sufficient; the e-mail address isn't necessary.
* It's helpful to add the bug/patch number as a comment:
XXX Describe the transmogrify() function added to the socket
(Contributed by P.Y. Developer in :issue:`12345`.)
This saves the maintainer the effort of going through the Mercurial log
when researching a change.
This article explains the new features in Python 3.3, compared to 3.2.
Python 3.3 was released on September 29, 2012. For full details,
see the `changelog <>`_.
.. seealso::
:pep:`398` - Python 3.3 Release Schedule
Summary -- Release highlights
.. This section singles out the most important changes in Python 3.3.
Brevity is key.
New syntax features:
* New ``yield from`` expression for :ref:`generator delegation <pep-380>`.
* The ``u'unicode'`` syntax is accepted again for :class:`str` objects.
New library modules:
* :mod:`faulthandler` (helps debugging low-level crashes)
* :mod:`ipaddress` (high-level objects representing IP addresses and masks)
* :mod:`lzma` (compress data using the XZ / LZMA algorithm)
* :mod:`unittest.mock` (replace parts of your system under test with mock objects)
* :mod:`venv` (Python :ref:`virtual environments <pep-405>`, as in the
popular ``virtualenv`` package)
New built-in features:
* Reworked :ref:`I/O exception hierarchy <pep-3151>`.
Implementation improvements:
* Rewritten :ref:`import machinery <importlib>` based on :mod:`importlib`.
* More compact :ref:`unicode strings <pep-393>`.
* More compact :ref:`attribute dictionaries <pep-412>`.
Significantly Improved Library Modules:
* C Accelerator for the :ref:`decimal <new-decimal>` module.
* Better unicode handling in the :ref:`email <new-email>` module
(:term:`provisional <provisional package>`).
Security improvements:
* Hash randomization is switched on by default.
Please read on for a comprehensive list of user-facing changes.
.. _pep-405:
PEP 405: Virtual Environments
Virtual environments help create separate Python setups while sharing a
system-wide base install, for ease of maintenance. Virtual environments
have their own set of private site packages (i.e. locally installed
libraries), and are optionally segregated from the system-wide site
packages. Their concept and implementation are inspired by the popular
``virtualenv`` third-party package, but benefit from tighter integration
with the interpreter core.
This PEP adds the :mod:`venv` module for programmatic access, and the
``pyvenv`` script for command-line access and
administration. The Python interpreter checks for a ``pyvenv.cfg``,
file whose existence signals the base of a virtual environment's directory
.. seealso::
:pep:`405` - Python Virtual Environments
PEP written by Carl Meyer; implementation by Carl Meyer and Vinay Sajip
PEP 420: Implicit Namespace Packages
Native support for package directories that don't require ````
marker files and can automatically span multiple path segments (inspired by
various third party approaches to namespace packages, as described in
.. seealso::
:pep:`420` - Implicit Namespace Packages
PEP written by Eric V. Smith; implementation by Eric V. Smith
and Barry Warsaw
.. _pep-3118-update:
PEP 3118: New memoryview implementation and buffer protocol documentation
The implementation of :pep:`3118` has been significantly improved.
The new memoryview implementation comprehensively fixes all ownership and
lifetime issues of dynamically allocated fields in the Py_buffer struct
that led to multiple crash reports. Additionally, several functions that
crashed or returned incorrect results for non-contiguous or multi-dimensional
input have been fixed.
The memoryview object now has a PEP-3118 compliant getbufferproc()
that checks the consumer's request type. Many new features have been
added, most of them work in full generality for non-contiguous arrays
and arrays with suboffsets.
The documentation has been updated, clearly spelling out responsibilities
for both exporters and consumers. Buffer request flags are grouped into
basic and compound flags. The memory layout of non-contiguous and
multi-dimensional NumPy-style arrays is explained.
* All native single character format specifiers in struct module syntax
(optionally prefixed with '@') are now supported.
* With some restrictions, the cast() method allows changing of format and
shape of C-contiguous arrays.
* Multi-dimensional list representations are supported for any array type.
* Multi-dimensional comparisons are supported for any array type.
* One-dimensional memoryviews of hashable (read-only) types with formats B,
b or c are now hashable. (Contributed by Antoine Pitrou in :issue:`13411`.)
* Arbitrary slicing of any 1-D arrays type is supported. For example, it
is now possible to reverse a memoryview in O(1) by using a negative step.
API changes
* The maximum number of dimensions is officially limited to 64.
* The representation of empty shape, strides and suboffsets is now
an empty tuple instead of ``None``.
* Accessing a memoryview element with format 'B' (unsigned bytes)
now returns an integer (in accordance with the struct module syntax).
For returning a bytes object the view must be cast to 'c' first.
* memoryview comparisons now use the logical structure of the operands
and compare all array elements by value. All format strings in struct
module syntax are supported. Views with unrecognised format strings
are still permitted, but will always compare as unequal, regardless
of view contents.
* For further changes see `Build and C API Changes`_ and `Porting C code`_.
(Contributed by Stefan Krah in :issue:`10181`.)
.. seealso::
:pep:`3118` - Revising the Buffer Protocol
.. _pep-393:
PEP 393: Flexible String Representation
The Unicode string type is changed to support multiple internal
representations, depending on the character with the largest Unicode ordinal
(1, 2, or 4 bytes) in the represented string. This allows a space-efficient
representation in common cases, but gives access to full UCS-4 on all
systems. For compatibility with existing APIs, several representations may
exist in parallel; over time, this compatibility should be phased out.
On the Python side, there should be no downside to this change.
On the C API side, :pep:`393` is fully backward compatible. The legacy API
should remain available at least five years. Applications using the legacy
API will not fully benefit of the memory reduction, or - worse - may use
a bit more memory, because Python may have to maintain two versions of each
string (in the legacy format and in the new efficient storage).
Changes introduced by :pep:`393` are the following:
* Python now always supports the full range of Unicode code points, including
non-BMP ones (i.e. from ``U+0000`` to ``U+10FFFF``). The distinction between
narrow and wide builds no longer exists and Python now behaves like a wide
build, even under Windows.
* With the death of narrow builds, the problems specific to narrow builds have
also been fixed, for example:
* :func:`len` now always returns 1 for non-BMP characters,
so ``len('\U0010FFFF') == 1``;
* surrogate pairs are not recombined in string literals,
so ``'\uDBFF\uDFFF' != '\U0010FFFF'``;
* indexing or slicing non-BMP characters returns the expected value,
so ``'\U0010FFFF'[0]`` now returns ``'\U0010FFFF'`` and not ``'\uDBFF'``;
* all other functions in the standard library now correctly handle
non-BMP code points.
* The value of :data:`sys.maxunicode` is now always ``1114111`` (``0x10FFFF``
in hexadecimal). The :c:func:`PyUnicode_GetMax` function still returns
either ``0xFFFF`` or ``0x10FFFF`` for backward compatibility, and it should
not be used with the new Unicode API (see :issue:`13054`).
* The :file:`./configure` flag ``--with-wide-unicode`` has been removed.
Performance and resource usage
The storage of Unicode strings now depends on the highest code point in the string:
* pure ASCII and Latin1 strings (``U+0000-U+00FF``) use 1 byte per code point;
* BMP strings (``U+0000-U+FFFF``) use 2 bytes per code point;
* non-BMP strings (``U+10000-U+10FFFF``) use 4 bytes per code point.
The net effect is that for most applications, memory usage of string
storage should decrease significantly - especially compared to former
wide unicode builds - as, in many cases, strings will be pure ASCII
even in international contexts (because many strings store non-human
language data, such as XML fragments, HTTP headers, JSON-encoded data,
etc.). We also hope that it will, for the same reasons, increase CPU
cache efficiency on non-trivial applications. The memory usage of
Python 3.3 is two to three times smaller than Python 3.2, and a little
bit better than Python 2.7, on a Django benchmark (see the PEP for
.. seealso::
:pep:`393` - Flexible String Representation
PEP written by Martin von Löwis; implementation by Torsten Becker
and Martin von Löwis.
.. _pep-397:
PEP 397: Python Launcher for Windows
The Python 3.3 Windows installer now includes a ``py`` launcher application
that can be used to launch Python applications in a version independent
This launcher is invoked implicitly when double-clicking ``*.py`` files.
If only a single Python version is installed on the system, that version
will be used to run the file. If multiple versions are installed, the most
recent version is used by default, but this can be overridden by including
a Unix-style "shebang line" in the Python script.
The launcher can also be used explicitly from the command line as the ``py``
application. Running ``py`` follows the same version selection rules as
implicitly launching scripts, but a more specific version can be selected
by passing appropriate arguments (such as ``-3`` to request Python 3 when
Python 2 is also installed, or ``-2.6`` to specifically request an earlier
Python version when a more recent version is installed).
In addition to the launcher, the Windows installer now includes an
option to add the newly installed Python to the system PATH. (Contributed
by Brian Curtin in :issue:`3561`.)
.. seealso::
:pep:`397` - Python Launcher for Windows
PEP written by Mark Hammond and Martin v. Löwis; implementation by
Vinay Sajip.
Launcher documentation: :ref:`launcher`
Installer PATH modification: :ref:`windows-path-mod`
.. _pep-3151:
PEP 3151: Reworking the OS and IO exception hierarchy
The hierarchy of exceptions raised by operating system errors is now both
simplified and finer-grained.
You don't have to worry anymore about choosing the appropriate exception
type between :exc:`OSError`, :exc:`IOError`, :exc:`EnvironmentError`,
:exc:`WindowsError`, :exc:`mmap.error`, :exc:`socket.error` or
:exc:`select.error`. All these exception types are now only one:
:exc:`OSError`. The other names are kept as aliases for compatibility
Also, it is now easier to catch a specific error condition. Instead of
inspecting the ``errno`` attribute (or ``args[0]``) for a particular
constant from the :mod:`errno` module, you can catch the adequate
:exc:`OSError` subclass. The available subclasses are the following:
* :exc:`BlockingIOError`
* :exc:`ChildProcessError`
* :exc:`ConnectionError`
* :exc:`FileExistsError`
* :exc:`FileNotFoundError`
* :exc:`InterruptedError`
* :exc:`IsADirectoryError`
* :exc:`NotADirectoryError`
* :exc:`PermissionError`
* :exc:`ProcessLookupError`
* :exc:`TimeoutError`
And the :exc:`ConnectionError` itself has finer-grained subclasses:
* :exc:`BrokenPipeError`
* :exc:`ConnectionAbortedError`
* :exc:`ConnectionRefusedError`
* :exc:`ConnectionResetError`
Thanks to the new exceptions, common usages of the :mod:`errno` can now be
avoided. For example, the following code written for Python 3.2::
from errno import ENOENT, EACCES, EPERM
with open("document.txt") as f:
content =
except IOError as err:
if err.errno == ENOENT:
print("document.txt file is missing")
elif err.errno in (EACCES, EPERM):
print("You are not allowed to read document.txt")
can now be written without the :mod:`errno` import and without manual
inspection of exception attributes::
with open("document.txt") as f:
content =
except FileNotFoundError:
print("document.txt file is missing")
except PermissionError:
print("You are not allowed to read document.txt")
.. seealso::
:pep:`3151` - Reworking the OS and IO Exception Hierarchy
PEP written and implemented by Antoine Pitrou
.. index::
single: yield; yield from (in What's New)
.. _pep-380:
PEP 380: Syntax for Delegating to a Subgenerator
PEP 380 adds the ``yield from`` expression, allowing a :term:`generator` to
part of its operations to another generator. This allows a section of code
containing :keyword:`yield` to be factored out and placed in another generator.
Additionally, the subgenerator is allowed to return with a value, and the
value is made available to the delegating generator.
While designed primarily for use in delegating to a subgenerator, the ``yield
from`` expression actually allows delegation to arbitrary subiterators.
For simple iterators, ``yield from iterable`` is essentially just a shortened
form of ``for item in iterable: yield item``::
>>> def g(x):
... yield from range(x, 0, -1)
... yield from range(x)
>>> list(g(5))
[5, 4, 3, 2, 1, 0, 1, 2, 3, 4]
However, unlike an ordinary loop, ``yield from`` allows subgenerators to
receive sent and thrown values directly from the calling scope, and
return a final value to the outer generator::
>>> def accumulate():
... tally = 0
... while 1:
... next = yield
... if next is None:
... return tally
... tally += next
>>> def gather_tallies(tallies):
... while 1:
... tally = yield from accumulate()
... tallies.append(tally)
>>> tallies = []
>>> acc = gather_tallies(tallies)
>>> next(acc) # Ensure the accumulator is ready to accept values
>>> for i in range(4):
... acc.send(i)
>>> acc.send(None) # Finish the first tally
>>> for i in range(5):
... acc.send(i)
>>> acc.send(None) # Finish the second tally
>>> tallies
[6, 10]
The main principle driving this change is to allow even generators that are
designed to be used with the ``send`` and ``throw`` methods to be split into
multiple subgenerators as easily as a single large function can be split into
multiple subfunctions.
.. seealso::
:pep:`380` - Syntax for Delegating to a Subgenerator
PEP written by Greg Ewing; implementation by Greg Ewing, integrated into
3.3 by Renaud Blanch, Ryan Kelly and Nick Coghlan; documentation by
Zbigniew Jędrzejewski-Szmek and Nick Coghlan
PEP 409: Suppressing exception context
PEP 409 introduces new syntax that allows the display of the chained
exception context to be disabled. This allows cleaner error messages in
applications that convert between exception types::
>>> class D:
... def __init__(self, extra):
... self._extra_attributes = extra
... def __getattr__(self, attr):
... try:
... return self._extra_attributes[attr]
... except KeyError:
... raise AttributeError(attr) from None
>>> D({}).x
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 8, in __getattr__
AttributeError: x
Without the ``from None`` suffix to suppress the cause, the original
exception would be displayed by default::
>>> class C:
... def __init__(self, extra):
... self._extra_attributes = extra
... def __getattr__(self, attr):
... try:
... return self._extra_attributes[attr]
... except KeyError:
... raise AttributeError(attr)
>>> C({}).x
Traceback (most recent call last):
File "<stdin>", line 6, in __getattr__
KeyError: 'x'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 8, in __getattr__
AttributeError: x
No debugging capability is lost, as the original exception context remains
available if needed (for example, if an intervening library has incorrectly
suppressed valuable underlying details)::
>>> try:
... D({}).x
... except AttributeError as exc:
... print(repr(exc.__context__))
.. seealso::
:pep:`409` - Suppressing exception context
PEP written by Ethan Furman; implemented by Ethan Furman and Nick
PEP 414: Explicit Unicode literals
To ease the transition from Python 2 for Unicode aware Python applications
that make heavy use of Unicode literals, Python 3.3 once again supports the
"``u``" prefix for string literals. This prefix has no semantic significance
in Python 3, it is provided solely to reduce the number of purely mechanical
changes in migrating to Python 3, making it easier for developers to focus on
the more significant semantic changes (such as the stricter default
separation of binary and text data).
.. seealso::
:pep:`414` - Explicit Unicode literals
PEP written by Armin Ronacher.
PEP 3155: Qualified name for classes and functions
Functions and class objects have a new ``__qualname__`` attribute representing
the "path" from the module top-level to their definition. For global functions
and classes, this is the same as ``__name__``. For other functions and classes,
it provides better information about where they were actually defined, and
how they might be accessible from the global scope.
Example with (non-bound) methods::
>>> class C:
... def meth(self):
... pass
>>> C.meth.__name__
>>> C.meth.__qualname__
Example with nested classes::
>>> class C:
... class D:
... def meth(self):
... pass
>>> C.D.__name__
>>> C.D.__qualname__
>>> C.D.meth.__name__
>>> C.D.meth.__qualname__
Example with nested functions::
>>> def outer():
... def inner():
... pass
... return inner
>>> outer().__name__
>>> outer().__qualname__
The string representation of those objects is also changed to include the
new, more precise information::
>>> str(C.D)
"<class '__main__.C.D'>"
>>> str(C.D.meth)
'<function C.D.meth at 0x7f46b9fe31e0>'
.. seealso::
:pep:`3155` - Qualified name for classes and functions
PEP written and implemented by Antoine Pitrou.
.. _pep-412:
PEP 412: Key-Sharing Dictionary
Dictionaries used for the storage of objects' attributes are now able to
share part of their internal storage between each other (namely, the part
which stores the keys and their respective hashes). This reduces the memory
consumption of programs creating many instances of non-builtin types.
.. seealso::
:pep:`412` - Key-Sharing Dictionary
PEP written and implemented by Mark Shannon.
PEP 362: Function Signature Object
A new function :func:`inspect.signature` makes introspection of python
callables easy and straightforward. A broad range of callables is supported:
python functions, decorated or not, classes, and :func:`functools.partial`
objects. New classes :class:`inspect.Signature`, :class:`inspect.Parameter`
and :class:`inspect.BoundArguments` hold information about the call signatures,
such as, annotations, default values, parameters kinds, and bound arguments,
which considerably simplifies writing decorators and any code that validates
or amends calling signatures or arguments.
.. seealso::
:pep:`362`: - Function Signature Object
PEP written by Brett Cannon, Yury Selivanov, Larry Hastings, Jiwon Seo;
implemented by Yury Selivanov.
PEP 421: Adding sys.implementation
A new attribute on the :mod:`sys` module exposes details specific to the
implementation of the currently running interpreter. The initial set of
attributes on :attr:`sys.implementation` are ``name``, ``version``,
``hexversion``, and ``cache_tag``.
The intention of ``sys.implementation`` is to consolidate into one namespace
the implementation-specific data used by the standard library. This allows
different Python implementations to share a single standard library code base
much more easily. In its initial state, ``sys.implementation`` holds only a
small portion of the implementation-specific data. Over time that ratio will
shift in order to make the standard library more portable.
One example of improved standard library portability is ``cache_tag``. As of
Python 3.3, ``sys.implementation.cache_tag`` is used by :mod:`importlib` to
support :pep:`3147` compliance. Any Python implementation that uses
``importlib`` for its built-in import system may use ``cache_tag`` to control
the caching behavior for modules.
The implementation of ``sys.implementation`` also introduces a new type to
Python: :class:`types.SimpleNamespace`. In contrast to a mapping-based
namespace, like :class:`dict`, ``SimpleNamespace`` is attribute-based, like
:class:`object`. However, unlike ``object``, ``SimpleNamespace`` instances
are writable. This means that you can add, remove, and modify the namespace
through normal attribute access.
.. seealso::
:pep:`421` - Adding sys.implementation
PEP written and implemented by Eric Snow.
.. _importlib:
Using importlib as the Implementation of Import
:issue:`2377` - Replace __import__ w/ importlib.__import__
:issue:`13959` - Re-implement parts of :mod:`!imp` in pure Python
:issue:`14605` - Make import machinery explicit
:issue:`14646` - Require loaders set __loader__ and __package__
The :func:`__import__` function is now powered by :func:`importlib.__import__`.
This work leads to the completion of "phase 2" of :pep:`302`. There are
multiple benefits to this change. First, it has allowed for more of the
machinery powering import to be exposed instead of being implicit and hidden
within the C code. It also provides a single implementation for all Python VMs
supporting Python 3.3 to use, helping to end any VM-specific deviations in
import semantics. And finally it eases the maintenance of import, allowing for
future growth to occur.
For the common user, there should be no visible change in semantics. For
those whose code currently manipulates import or calls import
programmatically, the code changes that might possibly be required are covered
in the `Porting Python code`_ section of this document.
New APIs
One of the large benefits of this work is the exposure of what goes into
making the import statement work. That means the various importers that were
once implicit are now fully exposed as part of the :mod:`importlib` package.
The abstract base classes defined in :mod:`` have been expanded
to properly delineate between :term:`meta path finders <meta path finder>`
and :term:`path entry finders <path entry finder>` by introducing
:class:`` and
:class:``, respectively. The old ABC of
:class:`!` is now only provided for backwards-compatibility
and does not enforce any method requirements.
In terms of finders, :class:`importlib.machinery.FileFinder` exposes the
mechanism used to search for source and bytecode files of a module. Previously
this class was an implicit member of :attr:`sys.path_hooks`.
For loaders, the new abstract base class :class:`` helps
write a loader that uses the file system as the storage mechanism for a module's
code. The loader for source files
(:class:`importlib.machinery.SourceFileLoader`), sourceless bytecode files
(:class:`importlib.machinery.SourcelessFileLoader`), and extension modules
(:class:`importlib.machinery.ExtensionFileLoader`) are now available for
direct use.
:exc:`ImportError` now has ``name`` and ``path`` attributes which are set when
there is relevant data to provide. The message for failed imports will also
provide the full name of the module now instead of just the tail end of the
module's name.
The :func:`importlib.invalidate_caches` function will now call the method with
the same name on all finders cached in :attr:`sys.path_importer_cache` to help
clean up any stored state as necessary.
Visible Changes
For potential required changes to code, see the `Porting Python code`_
Beyond the expanse of what :mod:`importlib` now exposes, there are other
visible changes to import. The biggest is that :attr:`sys.meta_path` and
:attr:`sys.path_hooks` now store all of the meta path finders and path entry
hooks used by import. Previously the finders were implicit and hidden within
the C code of import instead of being directly exposed. This means that one can
now easily remove or change the order of the various finders to fit one's needs.
Another change is that all modules have a ``__loader__`` attribute, storing the
loader used to create the module. :pep:`302` has been updated to make this
attribute mandatory for loaders to implement, so in the future once 3rd-party
loaders have been updated people will be able to rely on the existence of the
attribute. Until such time, though, import is setting the module post-load.
Loaders are also now expected to set the ``__package__`` attribute from
:pep:`366`. Once again, import itself is already setting this on all loaders
from :mod:`importlib` and import itself is setting the attribute post-load.
``None`` is now inserted into :attr:`sys.path_importer_cache` when no finder
can be found on :attr:`sys.path_hooks`. Since :class:`!imp.NullImporter` is not
directly exposed on :attr:`sys.path_hooks` it could no longer be relied upon to
always be available to use as a value representing no finder found.
All other changes relate to semantic changes which should be taken into
consideration when updating code for Python 3.3, and thus should be read about
in the `Porting Python code`_ section of this document.
(Implementation by Brett Cannon)
Other Language Changes
Some smaller changes made to the core Python language are:
* Added support for Unicode name aliases and named sequences.
Both :func:`unicodedata.lookup()` and ``'\N{...}'`` now resolve name aliases,
and :func:`unicodedata.lookup()` resolves named sequences too.
(Contributed by Ezio Melotti in :issue:`12753`.)
* Unicode database updated to UCD version 6.1.0
* Equality comparisons on :func:`range` objects now return a result reflecting
the equality of the underlying sequences generated by those range objects.
* The ``count()``, ``find()``, ``rfind()``, ``index()`` and ``rindex()``
methods of :class:`bytes` and :class:`bytearray` objects now accept an
integer between 0 and 255 as their first argument.
(Contributed by Petri Lehtinen in :issue:`12170`.)
* The ``rjust()``, ``ljust()``, and ``center()`` methods of :class:`bytes`
and :class:`bytearray` now accept a :class:`bytearray` for the ``fill``
argument. (Contributed by Petri Lehtinen in :issue:`12380`.)
* New methods have been added to :class:`list` and :class:`bytearray`:
``copy()`` and ``clear()`` (:issue:`10516`). Consequently,
:class:`` now also defines a
:meth:`` method (:issue:`11388`).
* Raw bytes literals can now be written ``rb"..."`` as well as ``br"..."``.
(Contributed by Antoine Pitrou in :issue:`13748`.)
* :meth:`dict.setdefault` now does only one lookup for the given key, making
it atomic when used with built-in types.
(Contributed by Filip Gruszczyński in :issue:`13521`.)
* The error messages produced when a function call does not match the function
signature have been significantly improved.
(Contributed by Benjamin Peterson.)
A Finer-Grained Import Lock
Previous versions of CPython have always relied on a global import lock.
This led to unexpected annoyances, such as deadlocks when importing a module
would trigger code execution in a different thread as a side-effect.
Clumsy workarounds were sometimes employed, such as the
:c:func:`PyImport_ImportModuleNoBlock` C API function.
In Python 3.3, importing a module takes a per-module lock. This correctly
serializes importation of a given module from multiple threads (preventing
the exposure of incompletely initialized modules), while eliminating the
aforementioned annoyances.
(Contributed by Antoine Pitrou in :issue:`9260`.)
Builtin functions and types
* :func:`open` gets a new *opener* parameter: the underlying file descriptor
for the file object is then obtained by calling *opener* with (*file*,
*flags*). It can be used to use custom flags like :data:`os.O_CLOEXEC` for
example. The ``'x'`` mode was added: open for exclusive creation, failing if
the file already exists.
* :func:`print`: added the *flush* keyword argument. If the *flush* keyword
argument is true, the stream is forcibly flushed.
* :func:`hash`: hash randomization is enabled by default, see
:meth:`object.__hash__` and :envvar:`PYTHONHASHSEED`.
* The :class:`str` type gets a new :meth:`~str.casefold` method: return a
casefolded copy of the string, casefolded strings may be used for caseless
matching. For example, ``'ß'.casefold()`` returns ``'ss'``.
* The sequence documentation has been substantially rewritten to better
explain the binary/text sequence distinction and to provide specific
documentation sections for the individual builtin sequence types
New Modules
This new debug module :mod:`faulthandler` contains functions to dump Python tracebacks explicitly,
on a fault (a crash like a segmentation fault), after a timeout, or on a user
signal. Call :func:`faulthandler.enable` to install fault handlers for the
:const:`SIGSEGV`, :const:`SIGFPE`, :const:`SIGABRT`, :const:`SIGBUS`, and
:const:`SIGILL` signals. You can also enable them at startup by setting the
:envvar:`PYTHONFAULTHANDLER` environment variable or by using :option:`-X`
``faulthandler`` command line option.
Example of a segmentation fault on Linux:
.. code-block:: shell-session
$ python -q -X faulthandler
>>> import ctypes
>>> ctypes.string_at(0)
Fatal Python error: Segmentation fault
Current thread 0x00007fb899f39700:
File "/home/python/cpython/Lib/ctypes/", line 486 in string_at
File "<stdin>", line 1 in <module>
Segmentation fault
The new :mod:`ipaddress` module provides tools for creating and manipulating
objects representing IPv4 and IPv6 addresses, networks and interfaces (i.e.
an IP address associated with a specific IP subnet).
(Contributed by Google and Peter Moody in :pep:`3144`.)
The newly added :mod:`lzma` module provides data compression and decompression
using the LZMA algorithm, including support for the ``.xz`` and ``.lzma``
file formats.
(Contributed by Nadeem Vawda and Per Øyvind Karlsen in :issue:`6715`.)
Improved Modules
Improved support for abstract base classes containing descriptors composed with
abstract methods. The recommended approach to declaring abstract descriptors is
now to provide :attr:`__isabstractmethod__` as a dynamically updated
property. The built-in descriptors have been updated accordingly.
* :class:`abc.abstractproperty` has been deprecated, use :class:`property`
with :func:`abc.abstractmethod` instead.
* :class:`abc.abstractclassmethod` has been deprecated, use
:class:`classmethod` with :func:`abc.abstractmethod` instead.
* :class:`abc.abstractstaticmethod` has been deprecated, use
:class:`staticmethod` with :func:`abc.abstractmethod` instead.
(Contributed by Darren Dale in :issue:`11610`.)
:meth:`abc.ABCMeta.register` now returns the registered subclass, which means
it can now be used as a class decorator (:issue:`10868`).
The :mod:`array` module supports the :c:expr:`long long` type using ``q`` and
``Q`` type codes.
(Contributed by Oren Tirosh and Hirokazu Yamamoto in :issue:`1172711`.)
ASCII-only Unicode strings are now accepted by the decoding functions of the
:mod:`base64` modern interface. For example, ``base64.b64decode('YWJj')``
returns ``b'abc'``. (Contributed by Catalin Iacob in :issue:`13641`.)
In addition to the binary objects they normally accept, the ``a2b_`` functions
now all also accept ASCII-only strings as input. (Contributed by Antoine
Pitrou in :issue:`13637`.)
The :mod:`bz2` module has been rewritten from scratch. In the process, several
new features have been added:
* New :func:`` function: open a bzip2-compressed file in binary or
text mode.
* :class:`bz2.BZ2File` can now read from and write to arbitrary file-like
objects, by means of its constructor's *fileobj* argument.
(Contributed by Nadeem Vawda in :issue:`5863`.)
* :class:`bz2.BZ2File` and :func:`bz2.decompress` can now decompress
multi-stream inputs (such as those produced by the :program:`pbzip2` tool).
:class:`bz2.BZ2File` can now also be used to create this type of file, using
the ``'a'`` (append) mode.
(Contributed by Nir Aides in :issue:`1625`.)
* :class:`bz2.BZ2File` now implements all of the :class:`io.BufferedIOBase` API,
except for the :meth:`detach` and :meth:`truncate` methods.
The :mod:`~encodings.mbcs` codec has been rewritten to handle correctly
``replace`` and ``ignore`` error handlers on all Windows versions. The
:mod:`~encodings.mbcs` codec now supports all error handlers, instead of only
``replace`` to encode and ``ignore`` to decode.
A new Windows-only codec has been added: ``cp65001`` (:issue:`13216`). It is the
Windows code page 65001 (Windows UTF-8, ``CP_UTF8``). For example, it is used
by ``sys.stdout`` if the console output code page is set to cp65001 (e.g., using
``chcp 65001`` command).
Multibyte CJK decoders now resynchronize faster. They only ignore the first
byte of an invalid byte sequence. For example, ``b'\xff\n'.decode('gb2312',
'replace')`` now returns a ``\n`` after the replacement character.
Incremental CJK codec encoders are no longer reset at each call to their
encode() methods. For example::
>>> import codecs
>>> encoder = codecs.getincrementalencoder('hz')('strict')
>>> b''.join(encoder.encode(x) for x in '\u52ff\u65bd\u65bc\u4eba\u3002 Bye.')
b'~{NpJ)l6HK!#~} Bye.'
This example gives ``b'~{Np~}~{J)~}~{l6~}~{HK~}~{!#~} Bye.'`` with older Python
The ``unicode_internal`` codec has been deprecated.
Addition of a new :class:`~collections.ChainMap` class to allow treating a
number of mappings as a single unit. (Written by Raymond Hettinger for
:issue:`11089`, made public in :issue:`11297`.)
The abstract base classes have been moved in a new :mod:``
module, to better differentiate between the abstract and the concrete
collections classes. Aliases for ABCs are still present in the
:mod:`collections` module to preserve existing imports. (:issue:`11085`)
.. XXX addition of __slots__ to ABCs not recorded here: internal detail
The :class:`~collections.Counter` class now supports the unary ``+`` and ``-``
operators, as well as the in-place operators ``+=``, ``-=``, ``|=``, and
``&=``. (Contributed by Raymond Hettinger in :issue:`13121`.)
:class:`~contextlib.ExitStack` now provides a solid foundation for
programmatic manipulation of context managers and similar cleanup
functionality. Unlike the previous ``contextlib.nested`` API (which was
deprecated and removed), the new API is designed to work correctly
regardless of whether context managers acquire their resources in
their ``__init__`` method (for example, file objects) or in their
``__enter__`` method (for example, synchronisation objects from the
:mod:`threading` module).
Addition of salt and modular crypt format (hashing method) and the :func:`~!crypt.mksalt`
function to the :mod:`!crypt` module.
* If the :mod:`curses` module is linked to the ncursesw library, use Unicode
functions when Unicode strings or characters are passed (e.g.
:c:func:`waddwstr`), and bytes functions otherwise (e.g. :c:func:`waddstr`).
* Use the locale encoding instead of ``utf-8`` to encode Unicode strings.
* :class:`curses.window` has a new :attr:`curses.window.encoding` attribute.
* The :class:`curses.window` class has a new :meth:`~curses.window.get_wch`
method to get a wide character
* The :mod:`curses` module has a new :meth:`~curses.unget_wch` function to
push a wide character so the next :meth:`~curses.window.get_wch` will return
(Contributed by Iñigo Serna in :issue:`6755`.)
* Equality comparisons between naive and aware :class:`~datetime.datetime`
instances now return :const:`False` instead of raising :exc:`TypeError`
* New :meth:`datetime.datetime.timestamp` method: Return POSIX timestamp
corresponding to the :class:`~datetime.datetime` instance.
* The :meth:`datetime.datetime.strftime` method supports formatting years
older than 1000.
* The :meth:`datetime.datetime.astimezone` method can now be
called without arguments to convert datetime instance to the system
.. _new-decimal:
:issue:`7652` - integrate fast native decimal arithmetic.
C-module and libmpdec written by Stefan Krah.
The new C version of the decimal module integrates the high speed libmpdec
library for arbitrary precision correctly rounded decimal floating point
arithmetic. libmpdec conforms to IBM's General Decimal Arithmetic Specification.
Performance gains range from 10x for database applications to 100x for
numerically intensive applications. These numbers are expected gains
for standard precisions used in decimal floating point arithmetic. Since
the precision is user configurable, the exact figures may vary. For example,
in integer bignum arithmetic the differences can be significantly higher.
The following table is meant as an illustration. Benchmarks are available
| | | _decimal | speedup |
| pi | 42.02s | 0.345s | 120x |
| telco | 172.19s | 5.68s | 30x |
| psycopg | 3.57s | 0.29s | 12x |
* The :exc:`~decimal.FloatOperation` signal optionally enables stricter
semantics for mixing floats and Decimals.
* If Python is compiled without threads, the C version automatically
disables the expensive thread local context machinery. In this case,
the variable :data:`~decimal.HAVE_THREADS` is set to ``False``.
API changes
* The C module has the following context limits, depending on the machine
| | 32-bit | 64-bit |
| :const:`MAX_PREC` | :const:`425000000` | :const:`999999999999999999` |
| :const:`MAX_EMAX` | :const:`425000000` | :const:`999999999999999999` |
| :const:`MIN_EMIN` | :const:`-425000000` | :const:`-999999999999999999` |
* In the context templates (:class:`~decimal.DefaultContext`,
:class:`~decimal.BasicContext` and :class:`~decimal.ExtendedContext`)
the magnitude of :attr:`~decimal.Context.Emax` and
:attr:`~decimal.Context.Emin` has changed to :const:`999999`.
* The :class:`~decimal.Decimal` constructor in does not observe
the context limits and converts values with arbitrary exponents or precision
exactly. Since the C version has internal limits, the following scheme is
used: If possible, values are converted exactly, otherwise
:exc:`~decimal.InvalidOperation` is raised and the result is NaN. In the
latter case it is always possible to use :meth:`~decimal.Context.create_decimal`
in order to obtain a rounded or inexact value.
* The power function in is always correctly rounded. In the
C version, it is defined in terms of the correctly rounded
:meth:`~decimal.Decimal.exp` and :meth:`~decimal.Decimal.ln` functions,
but the final result is only "almost always correctly rounded".
* In the C version, the context dictionary containing the signals is a
:class:``. For speed reasons,
:attr:`~decimal.Context.flags` and :attr:`~decimal.Context.traps` always
refer to the same :class:`` that the context
was initialized with. If a new signal dictionary is assigned,
:attr:`~decimal.Context.flags` and :attr:`~decimal.Context.traps`
are updated with the new values, but they do not reference the RHS
* Pickling a :class:`~decimal.Context` produces a different output in order
to have a common interchange format for the Python and C versions.
* The order of arguments in the :class:`~decimal.Context` constructor has been
changed to match the order displayed by :func:`repr`.
* The ``watchexp`` parameter in the :meth:`~decimal.Decimal.quantize` method
is deprecated.
.. _new-email:
Policy Framework
The email package now has a :mod:`~email.policy` framework. A
:class:`~email.policy.Policy` is an object with several methods and properties
that control how the email package behaves. The primary policy for Python 3.3
is the :class:`~email.policy.Compat32` policy, which provides backward
compatibility with the email package in Python 3.2. A ``policy`` can be
specified when an email message is parsed by a :mod:`~email.parser`, or when a
:class:`~email.message.Message` object is created, or when an email is
serialized using a :mod:`~email.generator`. Unless overridden, a policy passed
to a ``parser`` is inherited by all the ``Message`` object and sub-objects
created by the ``parser``. By default a ``generator`` will use the policy of
the ``Message`` object it is serializing. The default policy is
The minimum set of controls implemented by all ``policy`` objects are:
.. tabularcolumns:: |l|L|
=============== =======================================================
max_line_length The maximum length, excluding the linesep character(s),
individual lines may have when a ``Message`` is
serialized. Defaults to 78.
linesep The character used to separate individual lines when a
``Message`` is serialized. Defaults to ``\n``.
cte_type ``7bit`` or ``8bit``. ``8bit`` applies only to a
``Bytes`` ``generator``, and means that non-ASCII may
be used where allowed by the protocol (or where it
exists in the original input).
raise_on_defect Causes a ``parser`` to raise error when defects are
encountered instead of adding them to the ``Message``
object's ``defects`` list.
=============== =======================================================
A new policy instance, with new settings, is created using the
:meth:`~email.policy.Policy.clone` method of policy objects. ``clone`` takes
any of the above controls as keyword arguments. Any control not specified in
the call retains its default value. Thus you can create a policy that uses
``\r\n`` linesep characters like this::
mypolicy = compat32.clone(linesep='\r\n')
Policies can be used to make the generation of messages in the format needed by
your application simpler. Instead of having to remember to specify
``linesep='\r\n'`` in all the places you call a ``generator``, you can specify
it once, when you set the policy used by the ``parser`` or the ``Message``,
whichever your program uses to create ``Message`` objects. On the other hand,
if you need to generate messages in multiple forms, you can still specify the
parameters in the appropriate ``generator`` call. Or you can have custom
policy instances for your different cases, and pass those in when you create
the ``generator``.
Provisional Policy with New Header API
While the policy framework is worthwhile all by itself, the main motivation for
introducing it is to allow the creation of new policies that implement new
features for the email package in a way that maintains backward compatibility
for those who do not use the new policies. Because the new policies introduce a
new API, we are releasing them in Python 3.3 as a :term:`provisional policy
<provisional package>`. Backwards incompatible changes (up to and including
removal of the code) may occur if deemed necessary by the core developers.
The new policies are instances of :class:`~email.policy.EmailPolicy`,
and add the following additional controls:
.. tabularcolumns:: |l|L|
=============== =======================================================
refold_source Controls whether or not headers parsed by a
:mod:`~email.parser` are refolded by the
:mod:`~email.generator`. It can be ``none``, ``long``,
or ``all``. The default is ``long``, which means that
source headers with a line longer than
``max_line_length`` get refolded. ``none`` means no
line get refolded, and ``all`` means that all lines
get refolded.
header_factory A callable that take a ``name`` and ``value`` and
produces a custom header object.
=============== =======================================================
The ``header_factory`` is the key to the new features provided by the new
policies. When one of the new policies is used, any header retrieved from
a ``Message`` object is an object produced by the ``header_factory``, and any
time you set a header on a ``Message`` it becomes an object produced by
``header_factory``. All such header objects have a ``name`` attribute equal
to the header name. Address and Date headers have additional attributes
that give you access to the parsed data of the header. This means you can now
do things like this::
>>> m = Message(policy=SMTP)
>>> m['To'] = 'Éric <>'
>>> m['to']
'Éric <>'
>>> m['to'].addresses
(Address(display_name='Éric', username='foo', domain=''),)
>>> m['to'].addresses[0].username
>>> m['to'].addresses[0].display_name
>>> m['Date'] = email.utils.localtime()
>>> m['Date'].datetime
datetime.datetime(2012, 5, 25, 21, 39, 24, 465484, tzinfo=datetime.timezone(datetime.timedelta(-1, 72000), 'EDT'))
>>> m['Date']
'Fri, 25 May 2012 21:44:27 -0400'
>>> print(m)
To: =?utf-8?q?=C3=89ric?= <>
Date: Fri, 25 May 2012 21:44:27 -0400
You will note that the unicode display name is automatically encoded as
``utf-8`` when the message is serialized, but that when the header is accessed
directly, you get the unicode version. This eliminates any need to deal with
the :mod:`email.header` :meth:`~email.header.decode_header` or
:meth:`~email.header.make_header` functions.
You can also create addresses from parts::
>>> m['cc'] = [Group('pals', [Address('Bob', 'bob', ''),
... Address('Sally', 'sally', '')]),
... Address('Bonzo', addr_spec='')]
>>> print(m)
To: =?utf-8?q?=C3=89ric?= <>
Date: Fri, 25 May 2012 21:44:27 -0400
cc: pals: Bob <>, Sally <>;, Bonzo <>
Decoding to unicode is done automatically::
>>> m2 = message_from_string(str(m))
>>> m2['to']
'Éric <>'
When you parse a message, you can use the ``addresses`` and ``groups``
attributes of the header objects to access the groups and individual
>>> m2['cc'].addresses
(Address(display_name='Bob', username='bob', domain=''), Address(display_name='Sally', username='sally', domain=''), Address(display_name='Bonzo', username='bonz', domain=''))
>>> m2['cc'].groups
(Group(display_name='pals', addresses=(Address(display_name='Bob', username='bob', domain=''), Address(display_name='Sally', username='sally', domain='')), Group(display_name=None, addresses=(Address(display_name='Bonzo', username='bonz', domain=''),))
In summary, if you use one of the new policies, header manipulation works the
way it ought to: your application works with unicode strings, and the email
package transparently encodes and decodes the unicode to and from the RFC
standard Content Transfer Encodings.
Other API Changes
New :class:`~email.parser.BytesHeaderParser`, added to the :mod:`~email.parser`
module to complement :class:`~email.parser.HeaderParser` and complete the Bytes
New utility functions:
* :func:`~email.utils.format_datetime`: given a :class:`~datetime.datetime`,
produce a string formatted for use in an email header.
* :func:`~email.utils.parsedate_to_datetime`: given a date string from
an email header, convert it into an aware :class:`~datetime.datetime`,
or a naive :class:`~datetime.datetime` if the offset is ``-0000``.
* :func:`~email.utils.localtime`: With no argument, returns the
current local time as an aware :class:`~datetime.datetime` using the local
:class:`~datetime.timezone`. Given an aware :class:`~datetime.datetime`,
converts it into an aware :class:`~datetime.datetime` using the
local :class:`~datetime.timezone`.
* :class:`ftplib.FTP` now accepts a ``source_address`` keyword argument to
specify the ``(host, port)`` to use as the source address in the bind call
when creating the outgoing socket. (Contributed by Giampaolo Rodolà
in :issue:`8594`.)
* The :class:`~ftplib.FTP_TLS` class now provides a new
:func:`~ftplib.FTP_TLS.ccc` function to revert control channel back to
plaintext. This can be useful to take advantage of firewalls that know how
to handle NAT with non-secure FTP without opening fixed ports. (Contributed
by Giampaolo Rodolà in :issue:`12139`.)
* Added :meth:`ftplib.FTP.mlsd` method which provides a parsable directory
listing format and deprecates :meth:`ftplib.FTP.nlst` and
:meth:`ftplib.FTP.dir`. (Contributed by Giampaolo Rodolà in :issue:`11072`.)
The :func:`functools.lru_cache` decorator now accepts a ``typed`` keyword
argument (that defaults to ``False`` to ensure that it caches values of
different types that compare equal in separate cache slots. (Contributed
by Raymond Hettinger in :issue:`13227`.)
It is now possible to register callbacks invoked by the garbage collector
before and after collection using the new :data:`~gc.callbacks` list.
A new :func:`~hmac.compare_digest` function has been added to prevent side
channel attacks on digests through timing analysis. (Contributed by Nick
Coghlan and Christian Heimes in :issue:`15061`.)
:class:`http.server.BaseHTTPRequestHandler` now buffers the headers and writes
them all at once when :meth:`~http.server.BaseHTTPRequestHandler.end_headers` is
called. A new method :meth:`~http.server.BaseHTTPRequestHandler.flush_headers`
can be used to directly manage when the accumulated headers are sent.
(Contributed by Andrew Schaaf in :issue:`3709`.)
:class:`http.server` now produces valid ``HTML 4.01 strict`` output.
(Contributed by Ezio Melotti in :issue:`13295`.)
:class:`http.client.HTTPResponse` now has a
:meth:`~http.client.HTTPResponse.readinto` method, which means it can be used
as an :class:`io.RawIOBase` class. (Contributed by John Kuhn in
:class:`html.parser.HTMLParser` is now able to parse broken markup without
raising errors, therefore the *strict* argument of the constructor and the
:exc:`~html.parser.HTMLParseError` exception are now deprecated.
The ability to parse broken markup is the result of a number of bug fixes that
are also available on the latest bug fix releases of Python 2.7/3.2.
(Contributed by Ezio Melotti in :issue:`15114`, and :issue:`14538`,
:issue:`13993`, :issue:`13960`, :issue:`13358`, :issue:`1745761`,
:issue:`755670`, :issue:`13357`, :issue:`12629`, :issue:`1200313`,
:issue:`670664`, :issue:`13273`, :issue:`12888`, :issue:`7311`.)
A new :data:`~html.entities.html5` dictionary that maps HTML5 named character
references to the equivalent Unicode character(s) (e.g. ``html5['gt;'] ==
'>'``) has been added to the :mod:`html.entities` module. The dictionary is
now also used by :class:`~html.parser.HTMLParser`. (Contributed by Ezio
Melotti in :issue:`11113` and :issue:`15156`.)
The :class:`~imaplib.IMAP4_SSL` constructor now accepts an SSLContext
parameter to control parameters of the secure channel.
(Contributed by Sijin Joseph in :issue:`8808`.)
A new :func:`~inspect.getclosurevars` function has been added. This function
reports the current binding of all names referenced from the function body and
where those names were resolved, making it easier to verify correct internal
state when testing code that relies on stateful closures.
(Contributed by Meador Inge and Nick Coghlan in :issue:`13062`.)
A new :func:`~inspect.getgeneratorlocals` function has been added. This
function reports the current binding of local variables in the generator's
stack frame, making it easier to verify correct internal state when testing
(Contributed by Meador Inge in :issue:`15153`.)
The :func:`` function has a new ``'x'`` mode that can be used to
exclusively create a new file, and raise a :exc:`FileExistsError` if the file
already exists. It is based on the C11 'x' mode to fopen().
(Contributed by David Townshend in :issue:`12760`.)
The constructor of the :class:`~io.TextIOWrapper` class has a new
*write_through* optional argument. If *write_through* is ``True``, calls to
:meth:`~io.TextIOWrapper.write` are guaranteed not to be buffered: any data
written on the :class:`~io.TextIOWrapper` object is immediately handled to its
underlying binary buffer.
:func:`~itertools.accumulate` now takes an optional ``func`` argument for
providing a user-supplied binary function.
The :func:`~logging.basicConfig` function now supports an optional ``handlers``
argument taking an iterable of handlers to be added to the root logger.
A class level attribute :attr:`~logging.handlers.SysLogHandler.append_nul` has
been added to :class:`~logging.handlers.SysLogHandler` to allow control of the
appending of the ``NUL`` (``\000``) byte to syslog records, since for some
daemons it is required while for others it is passed through to the log.
The :mod:`math` module has a new function, :func:`~math.log2`, which returns
the base-2 logarithm of *x*.
(Written by Mark Dickinson in :issue:`11888`.)
The :meth:`` method is now more compatible with other file-like
objects: if the argument is omitted or specified as ``None``, it returns the
bytes from the current file position to the end of the mapping. (Contributed
by Petri Lehtinen in :issue:`12021`.)
The new :func:`multiprocessing.connection.wait` function allows polling
multiple objects (such as connections, sockets and pipes) with a timeout.
(Contributed by Richard Oudkerk in :issue:`12328`.)
:class:`multiprocessing.Connection` objects can now be transferred over
multiprocessing connections.
(Contributed by Richard Oudkerk in :issue:`4892`.)
:class:`multiprocessing.Process` now accepts a ``daemon`` keyword argument
to override the default behavior of inheriting the ``daemon`` flag from
the parent process (:issue:`6064`).
New attribute :data:`multiprocessing.Process.sentinel` allows a
program to wait on multiple :class:`~multiprocessing.Process` objects at one
time using the appropriate OS primitives (for example, :mod:`select` on
posix systems).
New methods :meth:`multiprocessing.pool.Pool.starmap` and
:meth:`~multiprocessing.pool.Pool.starmap_async` provide
:func:`itertools.starmap` equivalents to the existing
:meth:`` and
:meth:`~multiprocessing.pool.Pool.map_async` functions. (Contributed by Hynek
Schlawack in :issue:`12708`.)
The :class:`!nntplib.NNTP` class now supports the context management protocol to
unconditionally consume :exc:`socket.error` exceptions and to close the NNTP
connection when done::
>>> from nntplib import NNTP
>>> with NNTP('') as n:
('211 1755 1 1755 gmane.comp.python.committers', 1755, 1, 1755, 'gmane.comp.python.committers')
(Contributed by Giampaolo Rodolà in :issue:`9795`.)
* The :mod:`os` module has a new :func:`~os.pipe2` function that makes it
possible to create a pipe with :data:`~os.O_CLOEXEC` or
:data:`~os.O_NONBLOCK` flags set atomically. This is especially useful to
avoid race conditions in multi-threaded programs.
* The :mod:`os` module has a new :func:`~os.sendfile` function which provides
an efficient "zero-copy" way for copying data from one file (or socket)
descriptor to another. The phrase "zero-copy" refers to the fact that all of
the copying of data between the two descriptors is done entirely by the
kernel, with no copying of data into userspace buffers. :func:`~os.sendfile`
can be used to efficiently copy data from a file on disk to a network socket,
e.g. for downloading a file.
(Patch submitted by Ross Lagerwall and Giampaolo Rodolà in :issue:`10882`.)
* To avoid race conditions like symlink attacks and issues with temporary
files and directories, it is more reliable (and also faster) to manipulate
file descriptors instead of file names. Python 3.3 enhances existing functions
and introduces new functions to work on file descriptors (:issue:`4761`,
:issue:`10755` and :issue:`14626`).
- The :mod:`os` module has a new :func:`~os.fwalk` function similar to
:func:`~os.walk` except that it also yields file descriptors referring to the
directories visited. This is especially useful to avoid symlink races.
- The following functions get new optional *dir_fd* (:ref:`paths relative to
directory descriptors <dir_fd>`) and/or *follow_symlinks* (:ref:`not
following symlinks <follow_symlinks>`):
:func:`~os.access`, :func:`~os.chflags`, :func:`~os.chmod`, :func:`~os.chown`,
:func:``, :func:`~os.lstat`, :func:`~os.mkdir`, :func:`~os.mkfifo`,
:func:`~os.mknod`, :func:``, :func:`~os.readlink`, :func:`~os.remove`,
:func:`~os.rename`, :func:`~os.replace`, :func:`~os.rmdir`, :func:`~os.stat`,
:func:`~os.symlink`, :func:`~os.unlink`, :func:`~os.utime`. Platform
support for using these parameters can be checked via the sets
:data:`os.supports_dir_fd` and :data:`os.supports_follows_symlinks`.
- The following functions now support a file descriptor for their path argument:
:func:`~os.chdir`, :func:`~os.chmod`, :func:`~os.chown`,
:func:`~os.execve`, :func:`~os.listdir`, :func:`~os.pathconf`, :func:`~os.path.exists`,
:func:`~os.stat`, :func:`~os.statvfs`, :func:`~os.utime`. Platform support
for this can be checked via the :data:`os.supports_fd` set.
* :func:`~os.access` accepts an ``effective_ids`` keyword argument to turn on
using the effective uid/gid rather than the real uid/gid in the access check.
Platform support for this can be checked via the
:data:`~os.supports_effective_ids` set.
* The :mod:`os` module has two new functions: :func:`~os.getpriority` and
:func:`~os.setpriority`. They can be used to get or set process
niceness/priority in a fashion similar to :func:`os.nice` but extended to all
processes instead of just the current one.
(Patch submitted by Giampaolo Rodolà in :issue:`10784`.)
* The new :func:`os.replace` function allows cross-platform renaming of a
file with overwriting the destination. With :func:`os.rename`, an existing
destination file is overwritten under POSIX, but raises an error under
(Contributed by Antoine Pitrou in :issue:`8828`.)
* The stat family of functions (:func:`~os.stat`, :func:`~os.fstat`,
and :func:`~os.lstat`) now support reading a file's timestamps
with nanosecond precision. Symmetrically, :func:`~os.utime`
can now write file timestamps with nanosecond precision. (Contributed by
Larry Hastings in :issue:`14127`.)
* The new :func:`os.get_terminal_size` function queries the size of the
terminal attached to a file descriptor. See also
(Contributed by Zbigniew Jędrzejewski-Szmek in :issue:`13609`.)
.. XXX sort out this mess after beta1
* New functions to support Linux extended attributes (:issue:`12720`):
:func:`~os.getxattr`, :func:`~os.listxattr`, :func:`~os.removexattr`,
* New interface to the scheduler. These functions
control how a process is allocated CPU time by the operating system. New
:func:`~os.sched_get_priority_max`, :func:`~os.sched_get_priority_min`,
:func:`~os.sched_getaffinity`, :func:`~os.sched_getparam`,
:func:`~os.sched_getscheduler`, :func:`~os.sched_rr_get_interval`,
:func:`~os.sched_setaffinity`, :func:`~os.sched_setparam`,
:func:`~os.sched_setscheduler`, :func:`~os.sched_yield`,
* New functions to control the file system:
* :func:`~os.posix_fadvise`: Announces an intention to access data in a
specific pattern thus allowing the kernel to make optimizations.
* :func:`~os.posix_fallocate`: Ensures that enough disk space is allocated
for a file.
* :func:`~os.sync`: Force write of everything to disk.
* Additional new posix functions:
* :func:`~os.lockf`: Apply, test or remove a POSIX lock on an open file descriptor.
* :func:`~os.pread`: Read from a file descriptor at an offset, the file
offset remains unchanged.
* :func:`~os.pwrite`: Write to a file descriptor from an offset, leaving
the file offset unchanged.
* :func:`~os.readv`: Read from a file descriptor into a number of writable buffers.
* :func:`~os.truncate`: Truncate the file corresponding to *path*, so that
it is at most *length* bytes in size.
* :func:`~os.waitid`: Wait for the completion of one or more child processes.
* :func:`~os.writev`: Write the contents of *buffers* to a file descriptor,
where *buffers* is an arbitrary sequence of buffers.
* :func:`~os.getgrouplist` (:issue:`9344`): Return list of group ids that
specified user belongs to.
* :func:`~os.times` and :func:`~os.uname`: Return type changed from a tuple to
a tuple-like object with named attributes.
* Some platforms now support additional constants for the :func:`~os.lseek`
function, such as ``os.SEEK_HOLE`` and ``os.SEEK_DATA``.
* New constants :data:`~os.RTLD_LAZY`, :data:`~os.RTLD_NOW`,
:data:`~os.RTLD_GLOBAL`, :data:`~os.RTLD_LOCAL`, :data:`~os.RTLD_NODELETE`,
:data:`~os.RTLD_NOLOAD`, and :data:`~os.RTLD_DEEPBIND` are available on
platforms that support them. These are for use with the
:func:`sys.setdlopenflags` function, and supersede the similar constants
defined in :mod:`ctypes` and :mod:`DLFCN`. (Contributed by Victor Stinner
in :issue:`13226`.)
* :func:`os.symlink` now accepts (and ignores) the ``target_is_directory``
keyword argument on non-Windows platforms, to ease cross-platform support.
Tab-completion is now available not only for command names, but also their
arguments. For example, for the ``break`` command, function and file names
are completed.
(Contributed by Georg Brandl in :issue:`14210`)
:class:`pickle.Pickler` objects now have an optional
:attr:`~pickle.Pickler.dispatch_table` attribute allowing per-pickler
reduction functions to be set.
(Contributed by Richard Oudkerk in :issue:`14166`.)
The Tk GUI and the :func:`~pydoc.serve` function have been removed from the
:mod:`pydoc` module: ``pydoc -g`` and :func:`~pydoc.serve` have been deprecated
in Python 3.2.
:class:`str` regular expressions now support ``\u`` and ``\U`` escapes.
(Contributed by Serhiy Storchaka in :issue:`3665`.)
* :meth:`` now accepts a *blocking* parameter which when
set to false makes the method execute the scheduled events due to expire
soonest (if any) and then return immediately.
This is useful in case you want to use the :class:`~sched.scheduler` in
non-blocking applications. (Contributed by Giampaolo Rodolà in :issue:`13449`.)
* :class:`~sched.scheduler` class can now be safely used in multi-threaded
environments. (Contributed by Josiah Carlson and Giampaolo Rodolà in
* *timefunc* and *delayfunct* parameters of :class:`~sched.scheduler` class
constructor are now optional and defaults to :func:`time.time` and
:func:`time.sleep` respectively. (Contributed by Chris Clark in
* :meth:`~sched.scheduler.enter` and :meth:`~sched.scheduler.enterabs`
*argument* parameter is now optional. (Contributed by Chris Clark in
* :meth:`~sched.scheduler.enter` and :meth:`~sched.scheduler.enterabs`
now accept a *kwargs* parameter. (Contributed by Chris Clark in
Solaris and derivative platforms have a new class :class:`select.devpoll`
for high performance asynchronous sockets via :file:`/dev/poll`.
(Contributed by Jesús Cea Avión in :issue:`6397`.)
The previously undocumented helper function ``quote`` from the
:mod:`!pipes` modules has been moved to the :mod:`shlex` module and
documented. :func:`~shlex.quote` properly escapes all characters in a string
that might be otherwise given special meaning by the shell.
* New functions:
* :func:`~shutil.disk_usage`: provides total, used and free disk space
statistics. (Contributed by Giampaolo Rodolà in :issue:`12442`.)
* :func:`~shutil.chown`: allows one to change user and/or group of the given
path also specifying the user/group names and not only their numeric
ids. (Contributed by Sandro Tosi in :issue:`12191`.)
* :func:`shutil.get_terminal_size`: returns the size of the terminal window
to which the interpreter is attached. (Contributed by Zbigniew
Jędrzejewski-Szmek in :issue:`13609`.)
* :func:`~shutil.copy2` and :func:`~shutil.copystat` now preserve file
timestamps with nanosecond precision on platforms that support it.
They also preserve file "extended attributes" on Linux. (Contributed
by Larry Hastings in :issue:`14127` and :issue:`15238`.)
* Several functions now take an optional ``symlinks`` argument: when that
parameter is true, symlinks aren't dereferenced and the operation instead
acts on the symlink itself (or creates one, if relevant).
(Contributed by Hynek Schlawack in :issue:`12715`.)
* When copying files to a different file system, :func:`~shutil.move` now
handles symlinks the way the posix ``mv`` command does, recreating the
symlink rather than copying the target file contents. (Contributed by
Jonathan Niehof in :issue:`9993`.) :func:`~shutil.move` now also returns
the ``dst`` argument as its result.
* :func:`~shutil.rmtree` is now resistant to symlink attacks on platforms
which support the new ``dir_fd`` parameter in :func:`` and
:func:`os.unlink`. (Contributed by Martin von Löwis and Hynek Schlawack
in :issue:`4489`.)
* The :mod:`signal` module has new functions:
* :func:`~signal.pthread_sigmask`: fetch and/or change the signal mask of the
calling thread (Contributed by Jean-Paul Calderone in :issue:`8407`);
* :func:`~signal.pthread_kill`: send a signal to a thread;
* :func:`~signal.sigpending`: examine pending functions;
* :func:`~signal.sigwait`: wait a signal;
* :func:`~signal.sigwaitinfo`: wait for a signal, returning detailed
information about it;
* :func:`~signal.sigtimedwait`: like :func:`~signal.sigwaitinfo` but with a
* The signal handler writes the signal number as a single byte instead of
a nul byte into the wakeup file descriptor. So it is possible to wait more
than one signal and know which signals were raised.
* :func:`signal.signal` and :func:`signal.siginterrupt` raise an OSError,
instead of a RuntimeError: OSError has an errno attribute.
The :mod:`smtpd` module now supports :rfc:`5321` (extended SMTP) and :rfc:`1870`
(size extension). Per the standard, these extensions are enabled if and only
if the client initiates the session with an ``EHLO`` command.
(Initial ``ELHO`` support by Alberto Trevino. Size extension by Juhana
Jauhiainen. Substantial additional work on the patch contributed by Michele
Orrù and Dan Boswell. :issue:`8739`)
The :class:`~smtplib.SMTP`, :class:`~smtplib.SMTP_SSL`, and
:class:`~smtplib.LMTP` classes now accept a ``source_address`` keyword argument
to specify the ``(host, port)`` to use as the source address in the bind call
when creating the outgoing socket. (Contributed by Paulo Scardine in
:class:`~smtplib.SMTP` now supports the context management protocol, allowing an
``SMTP`` instance to be used in a ``with`` statement. (Contributed
by Giampaolo Rodolà in :issue:`11289`.)
The :class:`~smtplib.SMTP_SSL` constructor and the :meth:`~smtplib.SMTP.starttls`
method now accept an SSLContext parameter to control parameters of the secure
channel. (Contributed by Kasun Herath in :issue:`8809`.)
* The :class:`~socket.socket` class now exposes additional methods to process
ancillary data when supported by the underlying platform:
* :func:`~socket.socket.sendmsg`
* :func:`~socket.socket.recvmsg`
* :func:`~socket.socket.recvmsg_into`
(Contributed by David Watson in :issue:`6560`, based on an earlier patch by
Heiko Wundram)
* The :class:`~socket.socket` class now supports the PF_CAN protocol family
(, on Linux
(Contributed by Matthias Fuchs, updated by Tiago Gonçalves in :issue:`10141`.)
* The :class:`~socket.socket` class now supports the PF_RDS protocol family
( and
` <>`__).
* The :class:`~socket.socket` class now supports the ``PF_SYSTEM`` protocol
family on OS X. (Contributed by Michael Goderbauer in :issue:`13777`.)
* New function :func:`~socket.sethostname` allows the hostname to be set
on Unix systems if the calling process has sufficient privileges.
(Contributed by Ross Lagerwall in :issue:`10866`.)
:class:`~socketserver.BaseServer` now has an overridable method
:meth:`~socketserver.BaseServer.service_actions` that is called by the
:meth:`~socketserver.BaseServer.serve_forever` method in the service loop.
:class:`~socketserver.ForkingMixIn` now uses this to clean up zombie
child processes. (Contributed by Justin Warkentin in :issue:`11109`.)
New :class:`sqlite3.Connection` method
:meth:`~sqlite3.Connection.set_trace_callback` can be used to capture a trace of
all sql commands processed by sqlite. (Contributed by Torsten Landschoff
in :issue:`11688`.)
* The :mod:`ssl` module has two new random generation functions:
* :func:`~ssl.RAND_bytes`: generate cryptographically strong
pseudo-random bytes.
* :func:`~ssl.RAND_pseudo_bytes`: generate pseudo-random bytes.
(Contributed by Victor Stinner in :issue:`12049`.)
* The :mod:`ssl` module now exposes a finer-grained exception hierarchy
in order to make it easier to inspect the various kinds of errors.
(Contributed by Antoine Pitrou in :issue:`11183`.)
* :meth:`~ssl.SSLContext.load_cert_chain` now accepts a *password* argument
to be used if the private key is encrypted.
(Contributed by Adam Simpkins in :issue:`12803`.)
* Diffie-Hellman key exchange, both regular and Elliptic Curve-based, is
now supported through the :meth:`~ssl.SSLContext.load_dh_params` and
:meth:`~ssl.SSLContext.set_ecdh_curve` methods.
(Contributed by Antoine Pitrou in :issue:`13626` and :issue:`13627`.)
* SSL sockets have a new :meth:`~ssl.SSLSocket.get_channel_binding` method
allowing the implementation of certain authentication mechanisms such as
SCRAM-SHA-1-PLUS. (Contributed by Jacek Konieczny in :issue:`12551`.)
* You can query the SSL compression algorithm used by an SSL socket, thanks
to its new :meth:`~ssl.SSLSocket.compression` method. The new attribute
:attr:`~ssl.OP_NO_COMPRESSION` can be used to disable compression.
(Contributed by Antoine Pitrou in :issue:`13634`.)
* Support has been added for the Next Protocol Negotiation extension using
the :meth:`ssl.SSLContext.set_npn_protocols` method.
(Contributed by Colin Marc in :issue:`14204`.)
* SSL errors can now be introspected more easily thanks to
:attr:`~ssl.SSLError.library` and :attr:`~ssl.SSLError.reason` attributes.
(Contributed by Antoine Pitrou in :issue:`14837`.)
* The :func:`~ssl.get_server_certificate` function now supports IPv6.
(Contributed by Charles-François Natali in :issue:`11811`.)
* New attribute :attr:`~ssl.OP_CIPHER_SERVER_PREFERENCE` allows setting
SSLv3 server sockets to use the server's cipher ordering preference rather
than the client's (:issue:`13635`).
The undocumented tarfile.filemode function has been moved to
:func:`stat.filemode`. It can be used to convert a file's mode to a string of
the form '-rwxrwxrwx'.
(Contributed by Giampaolo Rodolà in :issue:`14807`.)
The :mod:`struct` module now supports ``ssize_t`` and ``size_t`` via the
new codes ``n`` and ``N``, respectively. (Contributed by Antoine Pitrou
in :issue:`3163`.)
Command strings can now be bytes objects on posix platforms. (Contributed by
Victor Stinner in :issue:`8513`.)
A new constant :data:`~subprocess.DEVNULL` allows suppressing output in a
platform-independent fashion. (Contributed by Ross Lagerwall in
The :mod:`sys` module has a new :data:`~sys.thread_info` :term:`named
tuple` holding information about the thread implementation
:mod:`tarfile` now supports ``lzma`` encoding via the :mod:`lzma` module.
(Contributed by Lars Gustäbel in :issue:`5689`.)
:meth:`~tempfile.SpooledTemporaryFile.truncate` method now accepts
a ``size`` parameter. (Contributed by Ryan Kelly in :issue:`9957`.)
The :mod:`textwrap` module has a new :func:`~textwrap.indent` that makes
it straightforward to add a common prefix to selected lines in a block
of text (:issue:`13857`).
:class:`threading.Condition`, :class:`threading.Semaphore`,
:class:`threading.BoundedSemaphore`, :class:`threading.Event`, and
:class:`threading.Timer`, all of which used to be factory functions returning a
class instance, are now classes and may be subclassed. (Contributed by Éric
Araujo in :issue:`10968`.)
The :class:`threading.Thread` constructor now accepts a ``daemon`` keyword
argument to override the default behavior of inheriting the ``daemon`` flag
value from the parent thread (:issue:`6064`).
The formerly private function ``_thread.get_ident`` is now available as the
public function :func:`threading.get_ident`. This eliminates several cases of
direct access to the ``_thread`` module in the stdlib. Third party code that
used ``_thread.get_ident`` should likewise be changed to use the new public
The :pep:`418` added new functions to the :mod:`time` module:
* :func:`~time.get_clock_info`: Get information on a clock.
* :func:`~time.monotonic`: Monotonic clock (cannot go backward), not affected
by system clock updates.
* :func:`~time.perf_counter`: Performance counter with the highest available
resolution to measure a short duration.
* :func:`~time.process_time`: Sum of the system and user CPU time of the
current process.
Other new functions:
* :func:`~time.clock_getres`, :func:`~time.clock_gettime` and
:func:`~time.clock_settime` functions with ``CLOCK_xxx`` constants.
(Contributed by Victor Stinner in :issue:`10278`.)
To improve cross platform consistency, :func:`~time.sleep` now raises a
:exc:`ValueError` when passed a negative sleep value. Previously this was an
error on posix, but produced an infinite sleep on Windows.
Add a new :class:`types.MappingProxyType` class: Read-only proxy of a mapping.
The new functions :func:`types.new_class` and :func:`types.prepare_class` provide support
for :pep:`3115` compliant dynamic type creation. (:issue:`14588`)
:meth:`.assertRaises`, :meth:`.assertRaisesRegex`, :meth:`.assertWarns`, and
:meth:`.assertWarnsRegex` now accept a keyword argument *msg* when used as
context managers. (Contributed by Ezio Melotti and Winston Ewert in
:meth:`` now returns the :class:`~unittest.TestResult`
The :class:`~urllib.request.Request` class, now accepts a *method* argument
used by :meth:`~urllib.request.Request.get_method` to determine what HTTP method
should be used. For example, this will send a ``'HEAD'`` request::
>>> urlopen(Request('', method='HEAD'))
The :mod:`webbrowser` module supports more "browsers": Google Chrome (named
:program:`chrome`, :program:`chromium`, :program:`chrome-browser` or
:program:`chromium-browser` depending on the version and operating system),
and the generic launchers :program:`xdg-open`, from the
project, and :program:`gvfs-open`, which is the default URI handler for GNOME
3. (The former contributed by Arnaud Calmettes in :issue:`13620`, the latter
by Matthias Klose in :issue:`14493`.)
The :mod:`xml.etree.ElementTree` module now imports its C accelerator by
default; there is no longer a need to explicitly import
:mod:`xml.etree.cElementTree` (this module stays for backwards compatibility,
but is now deprecated). In addition, the ``iter`` family of methods of
:class:`~xml.etree.ElementTree.Element` has been optimized (rewritten in C).
The module's documentation has also been greatly improved with added examples
and a more detailed reference.
New attribute :attr:`zlib.Decompress.eof` makes it possible to distinguish
between a properly formed compressed stream and an incomplete or truncated one.
(Contributed by Nadeem Vawda in :issue:`12646`.)
New attribute :attr:`zlib.ZLIB_RUNTIME_VERSION` reports the version string of
the underlying ``zlib`` library that is loaded at runtime. (Contributed by
Torsten Landschoff in :issue:`12306`.)
Major performance enhancements have been added:
* Thanks to :pep:`393`, some operations on Unicode strings have been optimized:
* the memory footprint is divided by 2 to 4 depending on the text
* encode an ASCII string to UTF-8 doesn't need to encode characters anymore,
the UTF-8 representation is shared with the ASCII representation
* the UTF-8 encoder has been optimized
* repeating a single ASCII letter and getting a substring of an ASCII string
is 4 times faster
* UTF-8 is now 2x to 4x faster. UTF-16 encoding is now up to 10x faster.
(Contributed by Serhiy Storchaka, :issue:`14624`, :issue:`14738` and
Build and C API Changes
Changes to Python's build process and to the C API include:
* New :pep:`3118` related function:
* :c:func:`PyMemoryView_FromMemory`
* :pep:`393` added new Unicode types, macros and functions:
* High-level API:
* :c:func:`PyUnicode_CopyCharacters`
* :c:func:`PyUnicode_FindChar`
* :c:func:`PyUnicode_GetLength`, :c:macro:`PyUnicode_GET_LENGTH`
* :c:func:`PyUnicode_New`
* :c:func:`PyUnicode_Substring`
* :c:func:`PyUnicode_ReadChar`, :c:func:`PyUnicode_WriteChar`
* Low-level API:
* :c:type:`Py_UCS1`, :c:type:`Py_UCS2`, :c:type:`Py_UCS4` types
* :c:type:`PyASCIIObject` and :c:type:`PyCompactUnicodeObject` structures
* :c:macro:`PyUnicode_READY`
* :c:func:`PyUnicode_FromKindAndData`
* :c:func:`PyUnicode_AsUCS4`, :c:func:`PyUnicode_AsUCS4Copy`
* :c:macro:`PyUnicode_DATA`, :c:macro:`PyUnicode_1BYTE_DATA`,
:c:macro:`PyUnicode_2BYTE_DATA`, :c:macro:`PyUnicode_4BYTE_DATA`
* :c:macro:`PyUnicode_KIND` with :c:type:`PyUnicode_Kind` enum:
:c:data:`PyUnicode_WCHAR_KIND`, :c:data:`PyUnicode_1BYTE_KIND`,
:c:data:`PyUnicode_2BYTE_KIND`, :c:data:`PyUnicode_4BYTE_KIND`
* :c:macro:`PyUnicode_READ`, :c:macro:`PyUnicode_READ_CHAR`, :c:macro:`PyUnicode_WRITE`
* :c:macro:`PyUnicode_MAX_CHAR_VALUE`
* :c:macro:`PyArg_ParseTuple` now accepts a :class:`bytearray` for the ``c``
format (:issue:`12380`).
Unsupported Operating Systems
OS/2 and VMS are no longer supported due to the lack of a maintainer.
Windows 2000 and Windows platforms which set ``COMSPEC`` to ````
are no longer supported due to maintenance burden.
OSF support, which was deprecated in 3.2, has been completely removed.
Deprecated Python modules, functions and methods
* Passing a non-empty string to ``object.__format__()`` is deprecated, and
will produce a :exc:`TypeError` in Python 3.4 (:issue:`9856`).
* The ``unicode_internal`` codec has been deprecated because of the
:pep:`393`, use UTF-8, UTF-16 (``utf-16-le`` or ``utf-16-be``), or UTF-32
(``utf-32-le`` or ``utf-32-be``)
* :meth:`ftplib.FTP.nlst` and :meth:`ftplib.FTP.dir`: use
* :func:`platform.popen`: use the :mod:`subprocess` module. Check especially
the :ref:`subprocess-replacements` section (:issue:`11377`).
* :issue:`13374`: The Windows bytes API has been deprecated in the :mod:`os`
module. Use Unicode filenames, instead of bytes filenames, to not depend on
the ANSI code page anymore and to support any filename.
* :issue:`13988`: The :mod:`xml.etree.cElementTree` module is deprecated. The
accelerator is used automatically whenever available.
* The behaviour of :func:`time.clock` depends on the platform: use the new
:func:`time.perf_counter` or :func:`time.process_time` function instead,
depending on your requirements, to have a well defined behaviour.
* The :func:`os.stat_float_times` function is deprecated.
* :mod:`abc` module:
* :class:`abc.abstractproperty` has been deprecated, use :class:`property`
with :func:`abc.abstractmethod` instead.
* :class:`abc.abstractclassmethod` has been deprecated, use
:class:`classmethod` with :func:`abc.abstractmethod` instead.
* :class:`abc.abstractstaticmethod` has been deprecated, use
:class:`staticmethod` with :func:`abc.abstractmethod` instead.
* :mod:`importlib` package:
* :meth:`` is now deprecated in favour of
:meth:`` as bytecode files now store
both the modification time and size of the source file the bytecode file was
compiled from.
Deprecated functions and types of the C API
The :c:type:`Py_UNICODE` has been deprecated by :pep:`393` and will be
removed in Python 4. All functions using this type are deprecated:
Unicode functions and methods using :c:type:`Py_UNICODE` and
:c:expr:`Py_UNICODE*` types:
* :c:macro:`PyUnicode_FromUnicode`: use :c:func:`PyUnicode_FromWideChar` or
* :c:macro:`PyUnicode_AS_UNICODE`, :c:func:`PyUnicode_AsUnicode`,
:c:func:`PyUnicode_AsUnicodeAndSize`: use :c:func:`PyUnicode_AsWideCharString`
* :c:macro:`PyUnicode_AS_DATA`: use :c:macro:`PyUnicode_DATA` with
:c:macro:`PyUnicode_READ` and :c:macro:`PyUnicode_WRITE`
* :c:macro:`PyUnicode_GET_SIZE`, :c:func:`PyUnicode_GetSize`: use
:c:macro:`PyUnicode_GET_LENGTH` or :c:func:`PyUnicode_GetLength`
* :c:macro:`PyUnicode_GET_DATA_SIZE`: use
``PyUnicode_GET_LENGTH(str) * PyUnicode_KIND(str)`` (only work on ready
* :c:func:`PyUnicode_AsUnicodeCopy`: use :c:func:`PyUnicode_AsUCS4Copy` or
* :c:func:`PyUnicode_GetMax`
Functions and macros manipulating Py_UNICODE* strings:
* :c:macro:`Py_UNICODE_strlen`: use :c:func:`PyUnicode_GetLength` or
* :c:macro:`Py_UNICODE_strcat`: use :c:func:`PyUnicode_CopyCharacters` or
* :c:macro:`Py_UNICODE_strcpy`, :c:macro:`Py_UNICODE_strncpy`,
:c:macro:`Py_UNICODE_COPY`: use :c:func:`PyUnicode_CopyCharacters` or
* :c:macro:`Py_UNICODE_strcmp`: use :c:func:`PyUnicode_Compare`
* :c:macro:`Py_UNICODE_strncmp`: use :c:func:`PyUnicode_Tailmatch`
* :c:macro:`Py_UNICODE_strchr`, :c:macro:`Py_UNICODE_strrchr`: use
* :c:macro:`Py_UNICODE_FILL`: use :c:func:`PyUnicode_Fill`
* :c:macro:`Py_UNICODE_MATCH`
* :c:func:`PyUnicode_Encode`: use :c:func:`PyUnicode_AsEncodedObject`
* :c:func:`PyUnicode_EncodeUTF7`
* :c:func:`PyUnicode_EncodeUTF8`: use :c:func:`PyUnicode_AsUTF8` or
* :c:func:`PyUnicode_EncodeUTF32`
* :c:func:`PyUnicode_EncodeUTF16`
* :c:func:`PyUnicode_EncodeUnicodeEscape` use
* :c:func:`PyUnicode_EncodeRawUnicodeEscape` use
* :c:func:`PyUnicode_EncodeLatin1`: use :c:func:`PyUnicode_AsLatin1String`
* :c:func:`PyUnicode_EncodeASCII`: use :c:func:`PyUnicode_AsASCIIString`
* :c:func:`PyUnicode_EncodeCharmap`
* :c:func:`PyUnicode_TranslateCharmap`
* :c:func:`PyUnicode_EncodeMBCS`: use :c:func:`PyUnicode_AsMBCSString` or
:c:func:`PyUnicode_EncodeCodePage` (with ``CP_ACP`` code_page)
* :c:func:`PyUnicode_EncodeDecimal`,
Deprecated features
The :mod:`array` module's ``'u'`` format code is now deprecated and will be
removed in Python 4 together with the rest of the (:c:type:`Py_UNICODE`) API.
Porting to Python 3.3
This section lists previously described changes and other bugfixes
that may require changes to your code.
.. _portingpythoncode:
Porting Python code
* Hash randomization is enabled by default. Set the :envvar:`PYTHONHASHSEED`
environment variable to ``0`` to disable hash randomization. See also the
:meth:`object.__hash__` method.
* :issue:`12326`: On Linux, sys.platform doesn't contain the major version
anymore. It is now always 'linux', instead of 'linux2' or 'linux3' depending
on the Linux version used to build Python. Replace sys.platform == 'linux2'
with sys.platform.startswith('linux'), or directly sys.platform == 'linux' if
you don't need to support older Python versions.
* :issue:`13847`, :issue:`14180`: :mod:`time` and :mod:`datetime`:
:exc:`OverflowError` is now raised instead of :exc:`ValueError` if a
timestamp is out of range. :exc:`OSError` is now raised if C functions
:c:func:`gmtime` or :c:func:`localtime` failed.
* The default finders used by import now utilize a cache of what is contained
within a specific directory. If you create a Python source file or sourceless
bytecode file, make sure to call :func:`importlib.invalidate_caches` to clear
out the cache for the finders to notice the new file.
* :exc:`ImportError` now uses the full name of the module that was attempted to
be imported. Doctests that check ImportErrors' message will need to be
updated to use the full name of the module instead of just the tail of the
* The *index* argument to :func:`__import__` now defaults to 0 instead of -1
and no longer support negative values. It was an oversight when :pep:`328` was
implemented that the default value remained -1. If you need to continue to
perform a relative import followed by an absolute import, then perform the
relative import using an index of 1, followed by another import using an
index of 0. It is preferred, though, that you use
:func:`importlib.import_module` rather than call :func:`__import__` directly.
* :func:`__import__` no longer allows one to use an index value other than 0
for top-level modules. E.g. ``__import__('sys', level=1)`` is now an error.
* Because :attr:`sys.meta_path` and :attr:`sys.path_hooks` now have finders on
them by default, you will most likely want to use :meth:`list.insert` instead
of :meth:`list.append` to add to those lists.
* Because ``None`` is now inserted into :attr:`sys.path_importer_cache`, if you
are clearing out entries in the dictionary of paths that do not have a
finder, you will need to remove keys paired with values of ``None`` **and**
:class:`!imp.NullImporter` to be backwards-compatible. This will lead to extra
overhead on older versions of Python that re-insert ``None`` into
:attr:`sys.path_importer_cache` where it represents the use of implicit
finders, but semantically it should not change anything.
* :class:`!` no longer specifies a ``find_module()`` abstract
method that must be implemented. If you were relying on subclasses to
implement that method, make sure to check for the method's existence first.
You will probably want to check for ``find_loader()`` first, though, in the
case of working with :term:`path entry finders <path entry finder>`.
* :mod:`pkgutil` has been converted to use :mod:`importlib` internally. This
eliminates many edge cases where the old behaviour of the :pep:`302` import
emulation failed to match the behaviour of the real import system. The
import emulation itself is still present, but is now deprecated. The
:func:`pkgutil.iter_importers` and :func:`pkgutil.walk_packages` functions
special case the standard import hooks so they are still supported even
though they do not provide the non-standard ``iter_modules()`` method.
* A longstanding RFC-compliance bug (:issue:`1079`) in the parsing done by
:func:`email.header.decode_header` has been fixed. Code that uses the
standard idiom to convert encoded headers into unicode
(``str(make_header(decode_header(h))``) will see no change, but code that
looks at the individual tuples returned by decode_header will see that
whitespace that precedes or follows ``ASCII`` sections is now included in the
``ASCII`` section. Code that builds headers using ``make_header`` should
also continue to work without change, since ``make_header`` continues to add
whitespace between ``ASCII`` and non-``ASCII`` sections if it is not already
present in the input strings.
* :func:`email.utils.formataddr` now does the correct content transfer
encoding when passed non-``ASCII`` display names. Any code that depended on
the previous buggy behavior that preserved the non-``ASCII`` unicode in the
formatted output string will need to be changed (:issue:`1690608`).
* :meth:`poplib.POP3.quit` may now raise protocol errors like all other
``poplib`` methods. Code that assumes ``quit`` does not raise
:exc:`poplib.error_proto` errors may need to be changed if errors on ``quit``
are encountered by a particular application (:issue:`11291`).
* The ``strict`` argument to :class:`email.parser.Parser`, deprecated since
Python 2.4, has finally been removed.
* The deprecated method ``unittest.TestCase.assertSameElements`` has been
* The deprecated variable ``time.accept2dyear`` has been removed.
* The deprecated ``Context._clamp`` attribute has been removed from the
:mod:`decimal` module. It was previously replaced by the public attribute
:attr:`~decimal.Context.clamp`. (See :issue:`8540`.)
* The undocumented internal helper class ``SSLFakeFile`` has been removed
from :mod:`smtplib`, since its functionality has long been provided directly
by :meth:`socket.socket.makefile`.
* Passing a negative value to :func:`time.sleep` on Windows now raises an
error instead of sleeping forever. It has always raised an error on posix.
* The ``ast.__version__`` constant has been removed. If you need to
make decisions affected by the AST version, use :attr:`sys.version_info`
to make the decision.
* Code that used to work around the fact that the :mod:`threading` module used
factory functions by subclassing the private classes will need to change to
subclass the now-public classes.
* The undocumented debugging machinery in the threading module has been
removed, simplifying the code. This should have no effect on production
code, but is mentioned here in case any application debug frameworks were
interacting with it (:issue:`13550`).
Porting C code
* In the course of changes to the buffer API the undocumented
:c:member:`~Py_buffer.smalltable` member of the
:c:type:`Py_buffer` structure has been removed and the
layout of the :c:type:`PyMemoryViewObject` has changed.
All extensions relying on the relevant parts in ``memoryobject.h``
or ``object.h`` must be rebuilt.
* Due to :ref:`PEP 393 <pep-393>`, the :c:type:`Py_UNICODE` type and all
functions using this type are deprecated (but will stay available for
at least five years). If you were using low-level Unicode APIs to
construct and access unicode objects and you want to benefit of the
memory footprint reduction provided by :pep:`393`, you have to convert
your code to the new :doc:`Unicode API <../c-api/unicode>`.
However, if you only have been using high-level functions such as
:c:func:`PyUnicode_Concat()`, :c:func:`PyUnicode_Join` or
:c:func:`PyUnicode_FromFormat()`, your code will automatically take
advantage of the new unicode representations.
* :c:func:`PyImport_GetMagicNumber` now returns ``-1`` upon failure.
* As a negative value for the *level* argument to :func:`__import__` is no
longer valid, the same now holds for :c:func:`PyImport_ImportModuleLevel`.
This also means that the value of *level* used by
:c:func:`PyImport_ImportModuleEx` is now ``0`` instead of ``-1``.
Building C extensions
* The range of possible file names for C extensions has been narrowed.
Very rarely used spellings have been suppressed: under POSIX, files
named ````, ```` and
``xxxmodule.cpython-*.so`` are no longer recognized as implementing
the ``xxx`` module. If you had been generating such files, you have
to switch to the other spellings (i.e., remove the ``module`` string
from the file names).
(implemented in :issue:`14040`.)
Command Line Switch Changes
* The -Q command-line flag and related artifacts have been removed. Code
checking sys.flags.division_warning will need updating.
(:issue:`10998`, contributed by Éric Araujo.)
* When :program:`python` is started with :option:`-S`, ``import site``
will no longer add site-specific paths to the module search paths. In
previous versions, it did.
(:issue:`11591`, contributed by Carl Meyer with editions by Éric Araujo.)