mirror of https://github.com/python/cpython
545 lines
17 KiB
ReStructuredText
545 lines
17 KiB
ReStructuredText
.. highlightlang:: none
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.. _using-on-general:
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Command line and environment
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============================
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The CPython interpreter scans the command line and the environment for various
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settings.
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.. note::
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Other implementations' command line schemes may differ. See
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:ref:`implementations` for further resources.
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.. _using-on-cmdline:
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Command line
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------------
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When invoking Python, you may specify any of these options::
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python [-dEiOQsStuUvxX3?] [-c command | -m module-name | script | - ] [args]
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The most common use case is, of course, a simple invocation of a script::
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python myscript.py
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.. _using-on-interface-options:
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Interface options
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~~~~~~~~~~~~~~~~~
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The interpreter interface resembles that of the UNIX shell, but provides some
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additional methods of invocation:
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* When called with standard input connected to a tty device, it prompts for
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commands and executes them until an EOF (an end-of-file character, you can
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produce that with *Ctrl-D* on UNIX or *Ctrl-Z, Enter* on Windows) is read.
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* When called with a file name argument or with a file as standard input, it
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reads and executes a script from that file.
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* When called with a directory name argument, it reads and executes an
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appropriately named script from that directory.
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* When called with ``-c command``, it executes the Python statement(s) given as
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*command*. Here *command* may contain multiple statements separated by
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newlines. Leading whitespace is significant in Python statements!
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* When called with ``-m module-name``, the given module is located on the
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Python module path and executed as a script.
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In non-interactive mode, the entire input is parsed before it is executed.
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An interface option terminates the list of options consumed by the interpreter,
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all consecutive arguments will end up in :data:`sys.argv` -- note that the first
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element, subscript zero (``sys.argv[0]``), is a string reflecting the program's
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source.
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.. cmdoption:: -c <command>
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Execute the Python code in *command*. *command* can be one ore more
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statements separated by newlines, with significant leading whitespace as in
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normal module code.
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If this option is given, the first element of :data:`sys.argv` will be
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``"-c"`` and the current directory will be added to the start of
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:data:`sys.path` (allowing modules in that directory to be imported as top
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level modules).
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.. cmdoption:: -m <module-name>
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Search :data:`sys.path` for the named module and execute its contents as
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the :mod:`__main__` module.
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Since the argument is a *module* name, you must not give a file extension
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(``.py``). The ``module-name`` should be a valid Python module name, but
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the implementation may not always enforce this (e.g. it may allow you to
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use a name that includes a hyphen).
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.. note::
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This option cannot be used with builtin modules and extension modules
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written in C, since they do not have Python module files. However, it
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can still be used for precompiled modules, even if the original source
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file is not available.
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If this option is given, the first element of :data:`sys.argv` will be the
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full path to the module file. As with the :option:`-c` option, the current
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directory will be added to the start of :data:`sys.path`.
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Many standard library modules contain code that is invoked on their execution
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as a script. An example is the :mod:`timeit` module::
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python -mtimeit -s 'setup here' 'benchmarked code here'
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python -mtimeit -h # for details
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.. seealso::
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:func:`runpy.run_module`
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The actual implementation of this feature.
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:pep:`338` -- Executing modules as scripts
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.. versionadded:: 2.4
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.. versionchanged:: 2.5
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The named module can now be located inside a package.
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.. describe:: -
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Read commands from standard input (:data:`sys.stdin`). If standard input is
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a terminal, :option:`-i` is implied.
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If this option is given, the first element of :data:`sys.argv` will be
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``"-"`` and the current directory will be added to the start of
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:data:`sys.path`.
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.. describe:: <script>
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Execute the Python code contained in *script*, which must be a filesystem
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path (absolute or relative) referring to either a Python file, a directory
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containing a ``__main__.py`` file, or a zipfile containing a
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``__main__.py`` file.
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If this option is given, the first element of :data:`sys.argv` will be the
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script name as given on the command line.
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If the script name refers directly to a Python file, the directory
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containing that file is added to the start of :data:`sys.path`, and the
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file is executed as the :mod:`__main__` module.
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If the script name refers to a directory or zipfile, the script name is
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added to the start of :data:`sys.path` and the ``__main__.py`` file in
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that location is executed as the :mod:`__main__` module.
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.. versionchanged:: 2.5
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Directories and zipfiles containing a ``__main__.py`` file at the top
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level are now considered valid Python scripts.
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If no interface option is given, :option:`-i` is implied, ``sys.argv[0]`` is
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an empty string (``""``) and the current directory will be added to the
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start of :data:`sys.path`.
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.. seealso:: :ref:`tut-invoking`
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Generic options
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~~~~~~~~~~~~~~~
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.. cmdoption:: -?
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-h
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--help
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Print a short description of all command line options.
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.. versionchanged:: 2.5
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The ``--help`` variant.
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.. cmdoption:: -V
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--version
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Print the Python version number and exit. Example output could be::
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Python 2.5.1
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.. versionchanged:: 2.5
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The ``--version`` variant.
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Miscellaneous options
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~~~~~~~~~~~~~~~~~~~~~
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.. cmdoption:: -B
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If given, Python won't try to write ``.pyc`` or ``.pyo`` files on the
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import of source modules. See also :envvar:`PYTHONDONTWRITEBYTECODE`.
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.. versionadded:: 2.6
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.. cmdoption:: -d
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Turn on parser debugging output (for wizards only, depending on compilation
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options). See also :envvar:`PYTHONDEBUG`.
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.. cmdoption:: -E
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Ignore all :envvar:`PYTHON*` environment variables, e.g.
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:envvar:`PYTHONPATH` and :envvar:`PYTHONHOME`, that might be set.
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.. versionadded:: 2.2
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.. cmdoption:: -i
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When a script is passed as first argument or the :option:`-c` option is used,
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enter interactive mode after executing the script or the command, even when
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:data:`sys.stdin` does not appear to be a terminal. The
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:envvar:`PYTHONSTARTUP` file is not read.
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This can be useful to inspect global variables or a stack trace when a script
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raises an exception. See also :envvar:`PYTHONINSPECT`.
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.. cmdoption:: -O
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Turn on basic optimizations. This changes the filename extension for
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compiled (:term:`bytecode`) files from ``.pyc`` to ``.pyo``. See also
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:envvar:`PYTHONOPTIMIZE`.
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.. cmdoption:: -OO
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Discard docstrings in addition to the :option:`-O` optimizations.
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.. cmdoption:: -Q <arg>
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Division control. The argument must be one of the following:
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``old``
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division of int/int and long/long return an int or long (*default*)
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``new``
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new division semantics, i.e. division of int/int and long/long returns a
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float
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``warn``
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old division semantics with a warning for int/int and long/long
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``warnall``
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old division semantics with a warning for all uses of the division operator
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.. seealso::
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:file:`Tools/scripts/fixdiv.py`
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for a use of ``warnall``
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:pep:`238` -- Changing the division operator
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.. cmdoption:: -s
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Don't add user site directory to sys.path
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.. versionadded:: 2.6
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.. seealso::
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:pep:`370` -- Per user site-packages directory
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.. cmdoption:: -S
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Disable the import of the module :mod:`site` and the site-dependent
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manipulations of :data:`sys.path` that it entails.
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.. cmdoption:: -t
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Issue a warning when a source file mixes tabs and spaces for indentation in a
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way that makes it depend on the worth of a tab expressed in spaces. Issue an
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error when the option is given twice (:option:`-tt`).
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.. cmdoption:: -u
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Force stdin, stdout and stderr to be totally unbuffered. On systems where it
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matters, also put stdin, stdout and stderr in binary mode.
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Note that there is internal buffering in :meth:`file.readlines` and
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:ref:`bltin-file-objects` (``for line in sys.stdin``) which is not influenced
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by this option. To work around this, you will want to use
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:meth:`file.readline` inside a ``while 1:`` loop.
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See also :envvar:`PYTHONUNBUFFERED`.
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.. XXX should the -U option be documented?
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.. cmdoption:: -v
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Print a message each time a module is initialized, showing the place
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(filename or built-in module) from which it is loaded. When given twice
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(:option:`-vv`), print a message for each file that is checked for when
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searching for a module. Also provides information on module cleanup at exit.
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See also :envvar:`PYTHONVERBOSE`.
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.. cmdoption:: -W arg
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Warning control. Python's warning machinery by default prints warning
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messages to :data:`sys.stderr`. A typical warning message has the following
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form::
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file:line: category: message
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By default, each warning is printed once for each source line where it
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occurs. This option controls how often warnings are printed.
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Multiple :option:`-W` options may be given; when a warning matches more than
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one option, the action for the last matching option is performed. Invalid
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:option:`-W` options are ignored (though, a warning message is printed about
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invalid options when the first warning is issued).
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Warnings can also be controlled from within a Python program using the
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:mod:`warnings` module.
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The simplest form of argument is one of the following action strings (or a
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unique abbreviation):
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``ignore``
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Ignore all warnings.
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``default``
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Explicitly request the default behavior (printing each warning once per
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source line).
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``all``
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Print a warning each time it occurs (this may generate many messages if a
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warning is triggered repeatedly for the same source line, such as inside a
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loop).
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``module``
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Print each warning only only the first time it occurs in each module.
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``once``
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Print each warning only the first time it occurs in the program.
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``error``
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Raise an exception instead of printing a warning message.
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The full form of argument is::
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action:message:category:module:line
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Here, *action* is as explained above but only applies to messages that match
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the remaining fields. Empty fields match all values; trailing empty fields
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may be omitted. The *message* field matches the start of the warning message
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printed; this match is case-insensitive. The *category* field matches the
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warning category. This must be a class name; the match test whether the
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actual warning category of the message is a subclass of the specified warning
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category. The full class name must be given. The *module* field matches the
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(fully-qualified) module name; this match is case-sensitive. The *line*
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field matches the line number, where zero matches all line numbers and is
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thus equivalent to an omitted line number.
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.. seealso::
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:mod:`warnings` -- the warnings module
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:pep:`230` -- Warning framework
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.. cmdoption:: -x
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Skip the first line of the source, allowing use of non-Unix forms of
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``#!cmd``. This is intended for a DOS specific hack only.
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.. warning:: The line numbers in error messages will be off by one!
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.. cmdoption:: -3
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Warn about Python 3.x incompatibilities. Among these are:
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* :meth:`dict.has_key`
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* :func:`apply`
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* :func:`callable`
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* :func:`coerce`
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* :func:`execfile`
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* :func:`reduce`
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* :func:`reload`
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Using these will emit a :exc:`DeprecationWarning`.
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.. versionadded:: 2.6
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.. _using-on-envvars:
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Environment variables
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---------------------
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These environment variables influence Python's behavior.
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.. envvar:: PYTHONHOME
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Change the location of the standard Python libraries. By default, the
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libraries are searched in :file:`{prefix}/lib/python{version}` and
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:file:`{exec_prefix}/lib/python{version}`, where :file:`{prefix}` and
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:file:`{exec_prefix}` are installation-dependent directories, both defaulting
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to :file:`/usr/local`.
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When :envvar:`PYTHONHOME` is set to a single directory, its value replaces
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both :file:`{prefix}` and :file:`{exec_prefix}`. To specify different values
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for these, set :envvar:`PYTHONHOME` to :file:`{prefix}:{exec_prefix}`.
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.. envvar:: PYTHONPATH
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Augment the default search path for module files. The format is the same as
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the shell's :envvar:`PATH`: one or more directory pathnames separated by
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:data:`os.pathsep` (e.g. colons on Unix or semicolons on Windows).
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Non-existent directories are silently ignored.
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In addition to normal directories, individual :envvar:`PYTHONPATH` entries
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may refer to zipfiles containing pure Python modules (in either source or
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compiled form). Extension modules cannot be imported from zipfiles.
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The default search path is installation dependent, but generally begins with
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:file:`{prefix}/lib/python{version}`` (see :envvar:`PYTHONHOME` above). It
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is *always* appended to :envvar:`PYTHONPATH`.
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An additional directory will be inserted in the search path in front of
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:envvar:`PYTHONPATH` as described above under
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:ref:`using-on-interface-options`. The search path can be manipulated from
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within a Python program as the variable :data:`sys.path`.
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.. envvar:: PYTHONSTARTUP
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If this is the name of a readable file, the Python commands in that file are
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executed before the first prompt is displayed in interactive mode. The file
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is executed in the same namespace where interactive commands are executed so
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that objects defined or imported in it can be used without qualification in
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the interactive session. You can also change the prompts :data:`sys.ps1` and
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:data:`sys.ps2` in this file.
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.. envvar:: PYTHONY2K
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Set this to a non-empty string to cause the :mod:`time` module to require
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dates specified as strings to include 4-digit years, otherwise 2-digit years
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are converted based on rules described in the :mod:`time` module
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documentation.
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.. envvar:: PYTHONOPTIMIZE
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If this is set to a non-empty string it is equivalent to specifying the
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:option:`-O` option. If set to an integer, it is equivalent to specifying
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:option:`-O` multiple times.
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.. envvar:: PYTHONDEBUG
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If this is set to a non-empty string it is equivalent to specifying the
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:option:`-d` option. If set to an integer, it is equivalent to specifying
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:option:`-d` multiple times.
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.. envvar:: PYTHONINSPECT
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If this is set to a non-empty string it is equivalent to specifying the
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:option:`-i` option.
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This variable can also be modified by Python code using :data:`os.environ`
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to force inspect mode on program termination.
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.. envvar:: PYTHONUNBUFFERED
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If this is set to a non-empty string it is equivalent to specifying the
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:option:`-u` option.
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.. envvar:: PYTHONVERBOSE
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If this is set to a non-empty string it is equivalent to specifying the
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:option:`-v` option. If set to an integer, it is equivalent to specifying
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:option:`-v` multiple times.
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.. envvar:: PYTHONCASEOK
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If this is set, Python ignores case in :keyword:`import` statements. This
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only works on Windows.
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.. envvar:: PYTHONDONTWRITEBYTECODE
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If this is set, Python won't try to write ``.pyc`` or ``.pyo`` files on the
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import of source modules.
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.. versionadded:: 2.6
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.. envvar:: PYTHONIOENCODING
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Overrides the encoding used for stdin/stdout/stderr, in the syntax
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``encodingname:errorhandler``. The ``:errorhandler`` part is optional and
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has the same meaning as in :func:`str.encode`.
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.. versionadded:: 2.6
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.. envvar:: PYTHONNOUSERSITE
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If this is set, Python won't add the user site directory to sys.path
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.. versionadded:: 2.6
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.. seealso::
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:pep:`370` -- Per user site-packages directory
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.. envvar:: PYTHONUSERBASE
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Sets the base directory for the user site directory
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.. versionadded:: 2.6
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.. seealso::
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:pep:`370` -- Per user site-packages directory
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.. envvar:: PYTHONEXECUTABLE
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If this environment variable is set, ``sys.argv[0]`` will be set to its
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value instead of the value got through the C runtime. Only works on
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Mac OS X.
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Debug-mode variables
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~~~~~~~~~~~~~~~~~~~~
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Setting these variables only has an effect in a debug build of Python, that is,
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if Python was configured with the :option:`--with-pydebug` build option.
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.. envvar:: PYTHONTHREADDEBUG
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If set, Python will print threading debug info.
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.. versionchanged:: 2.6
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Previously, this variable was called ``THREADDEBUG``.
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.. envvar:: PYTHONDUMPREFS
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If set, Python will dump objects and reference counts still alive after
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shutting down the interpreter.
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.. envvar:: PYTHONMALLOCSTATS
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If set, Python will print memory allocation statistics every time a new
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object arena is created, and on shutdown.
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