| .. _tut-appendix: |
| |
| ******** |
| Appendix |
| ******** |
| |
| |
| .. _tut-interac: |
| |
| Interactive Mode |
| ================ |
| |
| There are two variants of the interactive :term:`REPL`. The classic |
| basic interpreter is supported on all platforms with minimal line |
| control capabilities. |
| |
| On Windows, or Unix-like systems with :mod:`curses` support, |
| a new interactive shell is used by default. |
| This one supports color, multiline editing, history browsing, and |
| paste mode. To disable color, see :ref:`using-on-controlling-color` for |
| details. Function keys provide some additional functionality. |
| :kbd:`F1` enters the interactive help browser :mod:`pydoc`. |
| :kbd:`F2` allows for browsing command-line history with neither output nor the |
| :term:`>>>` and :term:`...` prompts. :kbd:`F3` enters "paste mode", which |
| makes pasting larger blocks of code easier. Press :kbd:`F3` to return to |
| the regular prompt. |
| |
| When using the new interactive shell, exit the shell by typing :kbd:`exit` |
| or :kbd:`quit`. Adding call parentheses after those commands is not |
| required. |
| |
| If the new interactive shell is not desired, it can be disabled via |
| the :envvar:`PYTHON_BASIC_REPL` environment variable. |
| |
| .. _tut-error: |
| |
| Error Handling |
| -------------- |
| |
| When an error occurs, the interpreter prints an error message and a stack trace. |
| In interactive mode, it then returns to the primary prompt; when input came from |
| a file, it exits with a nonzero exit status after printing the stack trace. |
| (Exceptions handled by an :keyword:`except` clause in a :keyword:`try` statement |
| are not errors in this context.) Some errors are unconditionally fatal and |
| cause an exit with a nonzero exit status; this applies to internal inconsistencies and |
| some cases of running out of memory. All error messages are written to the |
| standard error stream; normal output from executed commands is written to |
| standard output. |
| |
| Typing the interrupt character (usually :kbd:`Control-C` or :kbd:`Delete`) to the primary or |
| secondary prompt cancels the input and returns to the primary prompt. [#]_ |
| Typing an interrupt while a command is executing raises the |
| :exc:`KeyboardInterrupt` exception, which may be handled by a :keyword:`try` |
| statement. |
| |
| |
| .. _tut-scripts: |
| |
| Executable Python Scripts |
| ------------------------- |
| |
| On BSD'ish Unix systems, Python scripts can be made directly executable, like |
| shell scripts, by putting the line :: |
| |
| #!/usr/bin/env python3 |
| |
| (assuming that the interpreter is on the user's :envvar:`PATH`) at the beginning |
| of the script and giving the file an executable mode. The ``#!`` must be the |
| first two characters of the file. On some platforms, this first line must end |
| with a Unix-style line ending (``'\n'``), not a Windows (``'\r\n'``) line |
| ending. Note that the hash, or pound, character, ``'#'``, is used to start a |
| comment in Python. |
| |
| The script can be given an executable mode, or permission, using the |
| :program:`chmod` command. |
| |
| .. code-block:: shell-session |
| |
| $ chmod +x myscript.py |
| |
| On Windows systems, there is no notion of an "executable mode". The Python |
| installer automatically associates ``.py`` files with ``python.exe`` so that |
| a double-click on a Python file will run it as a script. The extension can |
| also be ``.pyw``, in that case, the console window that normally appears is |
| suppressed. |
| |
| |
| .. _tut-startup: |
| |
| The Interactive Startup File |
| ---------------------------- |
| |
| When you use Python interactively, it is frequently handy to have some standard |
| commands executed every time the interpreter is started. You can do this by |
| setting an environment variable named :envvar:`PYTHONSTARTUP` to the name of a |
| file containing your start-up commands. This is similar to the :file:`.profile` |
| feature of the Unix shells. |
| |
| This file is only read in interactive sessions, not when Python reads commands |
| from a script, and not when :file:`/dev/tty` is given as the explicit source of |
| commands (which otherwise behaves like an interactive session). It is executed |
| in the same namespace where interactive commands are executed, so that objects |
| that it defines or imports can be used without qualification in the interactive |
| session. You can also change the prompts ``sys.ps1`` and ``sys.ps2`` in this |
| file. |
| |
| If you want to read an additional start-up file from the current directory, you |
| can program this in the global start-up file using code like ``if |
| os.path.isfile('.pythonrc.py'): exec(open('.pythonrc.py').read())``. |
| If you want to use the startup file in a script, you must do this explicitly |
| in the script:: |
| |
| import os |
| filename = os.environ.get('PYTHONSTARTUP') |
| if filename and os.path.isfile(filename): |
| with open(filename) as fobj: |
| startup_file = fobj.read() |
| exec(startup_file) |
| |
| |
| .. _tut-customize: |
| |
| The Customization Modules |
| ------------------------- |
| |
| Python provides two hooks to let you customize it: :index:`sitecustomize` and |
| :index:`usercustomize`. To see how it works, you need first to find the location |
| of your user site-packages directory. Start Python and run this code:: |
| |
| >>> import site |
| >>> site.getusersitepackages() |
| '/home/user/.local/lib/python3.x/site-packages' |
| |
| Now you can create a file named :file:`usercustomize.py` in that directory and |
| put anything you want in it. It will affect every invocation of Python, unless |
| it is started with the :option:`-s` option to disable the automatic import. |
| |
| :index:`sitecustomize` works in the same way, but is typically created by an |
| administrator of the computer in the global site-packages directory, and is |
| imported before :index:`usercustomize`. See the documentation of the :mod:`site` |
| module for more details. |
| |
| |
| .. rubric:: Footnotes |
| |
| .. [#] A problem with the GNU Readline package may prevent this. |