Doc/c-api/veryhigh.rst

.. highlight:: c


.. _veryhigh:

*************************
The Very High Level Layer
*************************

The functions in this chapter will let you execute Python source code given in a
file or a buffer, but they will not let you interact in a more detailed way with
the interpreter.

Several of these functions accept a start symbol from the grammar as a
parameter.  The available start symbols are :c:data:`Py_eval_input`,
:c:data:`Py_file_input`, :c:data:`Py_single_input`, and
:c:data:`Py_func_type_input`.  These are described following the functions
which accept them as parameters.

Note also that several of these functions take :c:expr:`FILE*` parameters.  One
particular issue which needs to be handled carefully is that the :c:type:`FILE`
structure for different C libraries can be different and incompatible.  Under
Windows (at least), it is possible for dynamically linked extensions to actually
use different libraries, so care should be taken that :c:expr:`FILE*` parameters
are only passed to these functions if it is certain that they were created by
the same library that the Python runtime is using.


.. c:function:: int PyRun_AnyFile(FILE *fp, const char *filename)

   This is a simplified interface to :c:func:`PyRun_AnyFileExFlags` below, leaving
   *closeit* set to ``0`` and *flags* set to ``NULL``.


.. c:function:: int PyRun_AnyFileFlags(FILE *fp, const char *filename, PyCompilerFlags *flags)

   This is a simplified interface to :c:func:`PyRun_AnyFileExFlags` below, leaving
   the *closeit* argument set to ``0``.


.. c:function:: int PyRun_AnyFileEx(FILE *fp, const char *filename, int closeit)

   This is a simplified interface to :c:func:`PyRun_AnyFileExFlags` below, leaving
   the *flags* argument set to ``NULL``.


.. c:function:: int PyRun_AnyFileExFlags(FILE *fp, const char *filename, int closeit, PyCompilerFlags *flags)

   If *fp* refers to a file associated with an interactive device (console or
   terminal input or Unix pseudo-terminal), return the value of
   :c:func:`PyRun_InteractiveLoop`, otherwise return the result of
   :c:func:`PyRun_SimpleFile`.  *filename* is decoded from the filesystem
   encoding (:func:`sys.getfilesystemencoding`).  If *filename* is ``NULL``, this
   function uses ``"???"`` as the filename.
   If *closeit* is true, the file is closed before
   ``PyRun_SimpleFileExFlags()`` returns.


.. c:function:: int PyRun_SimpleString(const char *command)

   This is a simplified interface to :c:func:`PyRun_SimpleStringFlags` below,
   leaving the :c:struct:`PyCompilerFlags`\* argument set to ``NULL``.


.. c:function:: int PyRun_SimpleStringFlags(const char *command, PyCompilerFlags *flags)

   Executes the Python source code from *command* in the :mod:`__main__` module
   according to the *flags* argument. If :mod:`__main__` does not already exist, it
   is created.  Returns ``0`` on success or ``-1`` if an exception was raised.  If
   there was an error, there is no way to get the exception information. For the
   meaning of *flags*, see below.

   Note that if an otherwise unhandled :exc:`SystemExit` is raised, this
   function will not return ``-1``, but exit the process, as long as
   :c:member:`PyConfig.inspect` is zero.


.. c:function:: int PyRun_SimpleFile(FILE *fp, const char *filename)

   This is a simplified interface to :c:func:`PyRun_SimpleFileExFlags` below,
   leaving *closeit* set to ``0`` and *flags* set to ``NULL``.


.. c:function:: int PyRun_SimpleFileEx(FILE *fp, const char *filename, int closeit)

   This is a simplified interface to :c:func:`PyRun_SimpleFileExFlags` below,
   leaving *flags* set to ``NULL``.


.. c:function:: int PyRun_SimpleFileExFlags(FILE *fp, const char *filename, int closeit, PyCompilerFlags *flags)

   Similar to :c:func:`PyRun_SimpleStringFlags`, but the Python source code is read
   from *fp* instead of an in-memory string. *filename* should be the name of
   the file, it is decoded from :term:`filesystem encoding and error handler`.
   If *closeit* is true, the file is closed before
   ``PyRun_SimpleFileExFlags()`` returns.

   .. note::
      On Windows, *fp* should be opened as binary mode (e.g. ``fopen(filename, "rb")``).
      Otherwise, Python may not handle script file with LF line ending correctly.


.. c:function:: int PyRun_InteractiveOneObject(FILE *fp, PyObject *filename, PyCompilerFlags *flags)

   Read and execute a single statement from a file associated with an
   interactive device according to the *flags* argument.  The user will be
   prompted using ``sys.ps1`` and ``sys.ps2``. *filename* must be a Python
   :class:`str` object.

   Returns ``0`` when the input was
   executed successfully, ``-1`` if there was an exception, or an error code
   from the :file:`errcode.h` include file distributed as part of Python if
   there was a parse error.  (Note that :file:`errcode.h` is not included by
   :file:`Python.h`, so must be included specifically if needed.)


.. c:function:: int PyRun_InteractiveOne(FILE *fp, const char *filename)

   This is a simplified interface to :c:func:`PyRun_InteractiveOneFlags` below,
   leaving *flags* set to ``NULL``.


.. c:function:: int PyRun_InteractiveOneFlags(FILE *fp, const char *filename, PyCompilerFlags *flags)

   Similar to :c:func:`PyRun_InteractiveOneObject`, but *filename* is a
   :c:expr:`const char*`, which is decoded from the
   :term:`filesystem encoding and error handler`.


.. c:function:: int PyRun_InteractiveLoop(FILE *fp, const char *filename)

   This is a simplified interface to :c:func:`PyRun_InteractiveLoopFlags` below,
   leaving *flags* set to ``NULL``.


.. c:function:: int PyRun_InteractiveLoopFlags(FILE *fp, const char *filename, PyCompilerFlags *flags)

   Read and execute statements from a file associated with an interactive device
   until EOF is reached.  The user will be prompted using ``sys.ps1`` and
   ``sys.ps2``.  *filename* is decoded from the :term:`filesystem encoding and
   error handler`.  Returns ``0`` at EOF or a negative number upon failure.


.. c:var:: int (*PyOS_InputHook)(void)

   Can be set to point to a function with the prototype
   ``int func(void)``.  The function will be called when Python's
   interpreter prompt is about to become idle and wait for user input
   from the terminal.  The return value is ignored.  Overriding this
   hook can be used to integrate the interpreter's prompt with other
   event loops, as done in :file:`Modules/_tkinter.c` in the
   Python source code.

   .. versionchanged:: 3.12
      This function is only called from the
      :ref:`main interpreter <sub-interpreter-support>`.


.. c:var:: char* (*PyOS_ReadlineFunctionPointer)(FILE *, FILE *, const char *)

   Can be set to point to a function with the prototype
   ``char *func(FILE *stdin, FILE *stdout, char *prompt)``,
   overriding the default function used to read a single line of input
   at the interpreter's prompt.  The function is expected to output
   the string *prompt* if it's not ``NULL``, and then read a line of
   input from the provided standard input file, returning the
   resulting string.  For example, The :mod:`readline` module sets
   this hook to provide line-editing and tab-completion features.

   The result must be a string allocated by :c:func:`PyMem_RawMalloc` or
   :c:func:`PyMem_RawRealloc`, or ``NULL`` if an error occurred.

   .. versionchanged:: 3.4
      The result must be allocated by :c:func:`PyMem_RawMalloc` or
      :c:func:`PyMem_RawRealloc`, instead of being allocated by
      :c:func:`PyMem_Malloc` or :c:func:`PyMem_Realloc`.

   .. versionchanged:: 3.12
      This function is only called from the
      :ref:`main interpreter <sub-interpreter-support>`.

.. c:function:: PyObject* PyRun_String(const char *str, int start, PyObject *globals, PyObject *locals)

   This is a simplified interface to :c:func:`PyRun_StringFlags` below, leaving
   *flags* set to ``NULL``.


.. c:function:: PyObject* PyRun_StringFlags(const char *str, int start, PyObject *globals, PyObject *locals, PyCompilerFlags *flags)

   Execute Python source code from *str* in the context specified by the
   objects *globals* and *locals* with the compiler flags specified by
   *flags*.  *globals* must be a dictionary; *locals* can be any object
   that implements the mapping protocol.  The parameter *start* specifies
   the start symbol and must be one of the :ref:`available start symbols <start-symbols>`.

   Returns the result of executing the code as a Python object, or ``NULL`` if an
   exception was raised.


.. c:function:: PyObject* PyRun_File(FILE *fp, const char *filename, int start, PyObject *globals, PyObject *locals)

   This is a simplified interface to :c:func:`PyRun_FileExFlags` below, leaving
   *closeit* set to ``0`` and *flags* set to ``NULL``.


.. c:function:: PyObject* PyRun_FileEx(FILE *fp, const char *filename, int start, PyObject *globals, PyObject *locals, int closeit)

   This is a simplified interface to :c:func:`PyRun_FileExFlags` below, leaving
   *flags* set to ``NULL``.


.. c:function:: PyObject* PyRun_FileFlags(FILE *fp, const char *filename, int start, PyObject *globals, PyObject *locals, PyCompilerFlags *flags)

   This is a simplified interface to :c:func:`PyRun_FileExFlags` below, leaving
   *closeit* set to ``0``.


.. c:function:: PyObject* PyRun_FileExFlags(FILE *fp, const char *filename, int start, PyObject *globals, PyObject *locals, int closeit, PyCompilerFlags *flags)

   Similar to :c:func:`PyRun_StringFlags`, but the Python source code is read from
   *fp* instead of an in-memory string. *filename* should be the name of the file,
   it is decoded from the :term:`filesystem encoding and error handler`.
   If *closeit* is true, the file is closed before :c:func:`PyRun_FileExFlags`
   returns.


.. c:function:: PyObject* Py_CompileString(const char *str, const char *filename, int start)

   This is a simplified interface to :c:func:`Py_CompileStringFlags` below, leaving
   *flags* set to ``NULL``.


.. c:function:: PyObject* Py_CompileStringFlags(const char *str, const char *filename, int start, PyCompilerFlags *flags)

   This is a simplified interface to :c:func:`Py_CompileStringExFlags` below, with
   *optimize* set to ``-1``.


.. c:function:: PyObject* Py_CompileStringObject(const char *str, PyObject *filename, int start, PyCompilerFlags *flags, int optimize)

   Parse and compile the Python source code in *str*, returning the resulting code
   object.  The start symbol is given by *start*; this can be used to constrain the
   code which can be compiled and should be :ref:`available start symbols
   <start-symbols>`.  The filename specified by
   *filename* is used to construct the code object and may appear in tracebacks or
   :exc:`SyntaxError` exception messages.  This returns ``NULL`` if the code
   cannot be parsed or compiled.

   The integer *optimize* specifies the optimization level of the compiler; a
   value of ``-1`` selects the optimization level of the interpreter as given by
   :option:`-O` options.  Explicit levels are ``0`` (no optimization;
   ``__debug__`` is true), ``1`` (asserts are removed, ``__debug__`` is false)
   or ``2`` (docstrings are removed too).

   .. versionadded:: 3.4


.. c:function:: PyObject* Py_CompileStringExFlags(const char *str, const char *filename, int start, PyCompilerFlags *flags, int optimize)

   Like :c:func:`Py_CompileStringObject`, but *filename* is a byte string
   decoded from the :term:`filesystem encoding and error handler`.

   .. versionadded:: 3.2

.. c:function:: PyObject* PyEval_EvalCode(PyObject *co, PyObject *globals, PyObject *locals)

   This is a simplified interface to :c:func:`PyEval_EvalCodeEx`, with just
   the code object, and global and local variables.  The other arguments are
   set to ``NULL``.


.. c:function:: PyObject* PyEval_EvalCodeEx(PyObject *co, PyObject *globals, PyObject *locals, PyObject *const *args, int argcount, PyObject *const *kws, int kwcount, PyObject *const *defs, int defcount, PyObject *kwdefs, PyObject *closure)

   Evaluate a precompiled code object, given a particular environment for its
   evaluation.  This environment consists of a dictionary of global variables,
   a mapping object of local variables, arrays of arguments, keywords and
   defaults, a dictionary of default values for :ref:`keyword-only
   <keyword-only_parameter>` arguments and a closure tuple of cells.


.. c:function:: PyObject* PyEval_EvalFrame(PyFrameObject *f)

   Evaluate an execution frame.  This is a simplified interface to
   :c:func:`PyEval_EvalFrameEx`, for backward compatibility.


.. c:function:: PyObject* PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)

   This is the main, unvarnished function of Python interpretation.  The code
   object associated with the execution frame *f* is executed, interpreting
   bytecode and executing calls as needed.  The additional *throwflag*
   parameter can mostly be ignored - if true, then it causes an exception
   to immediately be thrown; this is used for the :meth:`~generator.throw`
   methods of generator objects.

   .. versionchanged:: 3.4
      This function now includes a debug assertion to help ensure that it
      does not silently discard an active exception.


.. c:function:: int PyEval_MergeCompilerFlags(PyCompilerFlags *cf)

   This function changes the flags of the current evaluation frame, and returns
   true on success, false on failure.


.. c:struct:: PyCompilerFlags

   This is the structure used to hold compiler flags.  In cases where code is only
   being compiled, it is passed as ``int flags``, and in cases where code is being
   executed, it is passed as ``PyCompilerFlags *flags``.  In this case, ``from
   __future__ import`` can modify *flags*.

   Whenever ``PyCompilerFlags *flags`` is ``NULL``, :c:member:`~PyCompilerFlags.cf_flags` is treated as
   equal to ``0``, and any modification due to ``from __future__ import`` is
   discarded.

   .. c:member:: int cf_flags

      Compiler flags.

   .. c:member:: int cf_feature_version

      *cf_feature_version* is the minor Python version. It should be
      initialized to ``PY_MINOR_VERSION``.

      The field is ignored by default, it is used if and only if
      ``PyCF_ONLY_AST`` flag is set in :c:member:`~PyCompilerFlags.cf_flags`.

   .. versionchanged:: 3.8
      Added *cf_feature_version* field.

   The available compiler flags are accessible as macros:

   .. c:namespace:: NULL

   .. c:macro:: PyCF_ALLOW_TOP_LEVEL_AWAIT
                PyCF_ONLY_AST
                PyCF_OPTIMIZED_AST
                PyCF_TYPE_COMMENTS

      See :ref:`compiler flags <ast-compiler-flags>` in documentation of the
      :py:mod:`!ast` Python module, which exports these constants under
      the same names.

   .. rubric:: Low-level flags

   The following flags and masks serve narrow needs of the standard
   library and interactive interpreters.  Code outside the standard
   library rarely has a reason to use them.  They are considered
   implementation details and may change at any time.

   .. c:macro:: PyCF_ALLOW_INCOMPLETE_INPUT

      This flag is a private interface between the compiler and the
      :mod:`codeop` module.  Do not use it; its behavior is unsupported
      and may change without warning.

      With this flag set, when compilation fails because the source text
      ends where more input is expected, for example in the middle of an
      indented block or an unterminated string literal, the error raised
      is the undocumented ``_IncompleteInputError``, a subclass of
      :exc:`SyntaxError`.  The :mod:`codeop` module sets this flag,
      together with :c:macro:`PyCF_DONT_IMPLY_DEDENT`, to tell input
      that is incomplete apart from input with a real syntax error, so
      that interactive interpreters know when to prompt for another
      line instead of reporting an error.

      .. versionadded:: 3.11

   .. c:macro:: PyCF_DONT_IMPLY_DEDENT

      By default, when compiling with the :c:var:`Py_single_input` start
      symbol, reaching the end of the source text implicitly closes any
      open indented blocks.  With this flag set, open blocks are only
      closed if the last line of the source ends with a newline; otherwise,
      compilation fails with a :exc:`SyntaxError`:

      .. code-block:: c

         PyCompilerFlags flags = {
             .cf_flags = 0,
             .cf_feature_version = PY_MINOR_VERSION,
         };
         const char *source = "if a:\n    pass";

         /* The "if" block is closed implicitly;
            this returns a code object: */
         Py_CompileStringFlags(source, "<input>", Py_single_input, &flags);

         /* With the flag, this fails with a SyntaxError,
            because the last line does not end with a newline: */
         flags.cf_flags = PyCF_DONT_IMPLY_DEDENT;
         Py_CompileStringFlags(source, "<input>", Py_single_input, &flags);

      The :mod:`codeop` module uses this flag to detect incomplete
      interactive input.  While the user is still typing inside an
      indented block, the source does not yet end with a newline, so it
      fails to compile and the user is prompted for another line.

   .. c:macro:: PyCF_IGNORE_COOKIE

      Read the source text as UTF-8, ignoring its :pep:`263` encoding
      declaration ("coding cookie"), if any:

      .. code-block:: c

         PyCompilerFlags flags = {
             .cf_flags = 0,
             .cf_feature_version = PY_MINOR_VERSION,
         };
         const char *source = "# coding: latin-1\ns = '\xe9'\n";

         /* The coding cookie is honored: byte 0xE9 is decoded as
            Latin-1, and this returns a code object that sets s to "é": */
         Py_CompileStringFlags(source, "<input>", Py_file_input, &flags);

         /* With the flag, the cookie is ignored and compilation fails
            with a SyntaxError, because 0xE9 is not valid UTF-8: */
         flags.cf_flags = PyCF_IGNORE_COOKIE;
         Py_CompileStringFlags(source, "<input>", Py_file_input, &flags);

      The :func:`compile`, :func:`eval` and :func:`exec` built-in functions
      set this flag when the source is a :class:`str` object, because they
      pass the text to the parser encoded as UTF-8.

   .. c:macro:: PyCF_SOURCE_IS_UTF8

      Mark the source text as known to be UTF-8 encoded.
      The :func:`compile`, :func:`eval` and :func:`exec` built-in functions
      set this flag, but it currently has no effect.

   The "``PyCF``" flags above can be combined with "``CO_FUTURE``" flags such
   as :c:macro:`CO_FUTURE_ANNOTATIONS` to enable features normally
   selectable using :ref:`future statements <future>`.
   See :ref:`c_codeobject_flags` for a complete list.

   The following masks combine several flags:

   .. c:macro:: PyCF_MASK

      Bitmask of all ``CO_FUTURE`` flags (see :ref:`c_codeobject_flags`),
      which select features normally enabled by
      :ref:`future statements <future>`.
      When code compiled with a ``PyCompilerFlags *flags`` argument
      contains a ``from __future__ import`` statement, the flag for the
      imported feature is added to *flags*, so that code executed later
      in the same context inherits it.

   .. c:macro:: PyCF_MASK_OBSOLETE

      Do not use this mask in new code.  It is kept only so that old
      code passing its flags to :func:`compile` keeps working.

      Bitmask of flags for obsolete future features that no longer
      have any effect.

   .. c:macro:: PyCF_COMPILE_MASK

      Bitmask of all ``PyCF`` flags that change how the source is
      compiled, such as :c:macro:`PyCF_ONLY_AST`.
      The :func:`compile` built-in function uses this mask to validate
      its *flags* argument.


.. _start-symbols:

Available start symbols
^^^^^^^^^^^^^^^^^^^^^^^


.. c:var:: int Py_eval_input

   .. index:: single: Py_CompileString (C function)

   The start symbol from the Python grammar for isolated expressions; for use with
   :c:func:`Py_CompileString`.


.. c:var:: int Py_file_input

   .. index:: single: Py_CompileString (C function)

   The start symbol from the Python grammar for sequences of statements as read
   from a file or other source; for use with :c:func:`Py_CompileString`.  This is
   the symbol to use when compiling arbitrarily long Python source code.


.. c:var:: int Py_single_input

   .. index:: single: Py_CompileString (C function)

   The start symbol from the Python grammar for a single statement; for use with
   :c:func:`Py_CompileString`. This is the symbol used for the interactive
   interpreter loop.


.. c:var:: int Py_func_type_input

   .. index:: single: Py_CompileString (C function)

   The start symbol from the Python grammar for a function type; for use with
   :c:func:`Py_CompileString`. This is used to parse "signature type comments"
   from :pep:`484`.

   This requires the :c:macro:`PyCF_ONLY_AST` flag to be set.

   .. seealso::
      * :py:class:`ast.FunctionType`
      * :pep:`484`

   .. versionadded:: 3.8


Stack Effects
^^^^^^^^^^^^^

.. seealso::
   :py:func:`dis.stack_effect`


.. c:macro:: PY_INVALID_STACK_EFFECT

   Sentinel value representing an invalid stack effect.

   This is currently equivalent to ``INT_MAX``.

   .. versionadded:: 3.8


.. c:function:: int PyCompile_OpcodeStackEffect(int opcode, int oparg)

   Compute the stack effect of *opcode* with argument *oparg*.

   On success, this function returns the stack effect; on failure, this
   returns :c:macro:`PY_INVALID_STACK_EFFECT`.

   .. versionadded:: 3.4


.. c:function:: int PyCompile_OpcodeStackEffectWithJump(int opcode, int oparg, int jump)

   Similar to :c:func:`PyCompile_OpcodeStackEffect`, but don't include the
   stack effect of jumping if *jump* is zero.

   If *jump* is ``0``, this will not include the stack effect of jumping, but
   if *jump* is ``1`` or ``-1``, this will include it.

   On success, this function returns the stack effect; on failure, this
   returns :c:macro:`PY_INVALID_STACK_EFFECT`.

   .. versionadded:: 3.8