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			* Cannot seem to link directly to main options from the “unittest” module, because that module has its own set of options * Mask out linking for options that no longer exist in Python 3
		
			
				
	
	
		
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			643 lines
		
	
	
	
		
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			ReStructuredText
		
	
	
	
	
	
| .. highlightlang:: sh
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| 
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| .. ATTENTION: You probably should update Misc/python.man, too, if you modify
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|    this file.
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| 
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| .. _using-on-general:
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| 
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| Command line and environment
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| ============================
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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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| 
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| .. impl-detail::
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| 
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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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| 
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| 
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| .. _using-on-cmdline:
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| 
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| Command line
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| ------------
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| 
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| When invoking Python, you may specify any of these options::
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| 
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|     python [-bBdEhiIOqsSuvVWx?] [-c command | -m module-name | script | - ] [args]
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| 
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| The most common use case is, of course, a simple invocation of a script::
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| 
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|     python myscript.py
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| 
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| 
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| .. _using-on-interface-options:
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| 
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| Interface options
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| ~~~~~~~~~~~~~~~~~
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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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| 
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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 :kbd:`Ctrl-D` on UNIX or :kbd:`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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| 
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| In non-interactive mode, the entire input is parsed before it is executed.
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| 
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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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| 
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| .. cmdoption:: -c <command>
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| 
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|    Execute the Python code in *command*.  *command* can be one or 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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| 
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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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| 
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| 
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| .. cmdoption:: -m <module-name>
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| 
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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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| 
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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 absolute 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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| 
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|    Package names (including namespace packages) are also permitted. When a
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|    package name is supplied instead
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|    of a normal module, the interpreter will execute ``<pkg>.__main__`` as
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|    the main module. This behaviour is deliberately similar to the handling
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|    of directories and zipfiles that are passed to the interpreter as the
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|    script argument.
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| 
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|    .. note::
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| 
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|       This option cannot be used with built-in 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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| 
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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 (while the module file is being located, the
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|    first element will be set to ``"-m"``). As with the :option:`-c` option,
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|    the current directory will be added to the start of :data:`sys.path`.
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| 
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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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| 
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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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| 
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|    .. seealso::
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|       :func:`runpy.run_module`
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|          Equivalent functionality directly available to Python code
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| 
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|       :pep:`338` -- Executing modules as scripts
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| 
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| 
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|    .. versionchanged:: 3.1
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|       Supply the package name to run a ``__main__`` submodule.
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| 
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|    .. versionchanged:: 3.4
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|       namespace packages are also supported
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| 
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| 
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| .. describe:: -
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| 
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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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| 
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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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| 
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| 
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| .. describe:: <script>
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| 
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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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| 
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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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| 
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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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| 
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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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| 
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|    .. seealso::
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|       :func:`runpy.run_path`
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|          Equivalent functionality directly available to Python code
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| 
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| 
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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`.  Also, tab-completion and history editing is
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| automatically enabled, if available on your platform (see
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| :ref:`rlcompleter-config`).
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| 
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| .. seealso::  :ref:`tut-invoking`
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| 
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| .. versionchanged:: 3.4
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|    Automatic enabling of tab-completion and history editing.
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| 
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| 
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| Generic options
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| ~~~~~~~~~~~~~~~
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| 
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| .. cmdoption:: -?
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|                -h
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|                --help
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| 
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|    Print a short description of all command line options.
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| 
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| 
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| .. cmdoption:: -V
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|                --version
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| 
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|    Print the Python version number and exit.  Example output could be::
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| 
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|        Python 3.0
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| 
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| 
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| .. _using-on-misc-options:
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| 
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| Miscellaneous options
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| ~~~~~~~~~~~~~~~~~~~~~
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| 
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| .. cmdoption:: -b
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| 
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|    Issue a warning when comparing :class:`bytes` or :class:`bytearray` with
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|    :class:`str` or :class:`bytes` with :class:`int`.  Issue an error when the
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|    option is given twice (:option:`!-bb`).
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| 
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|    .. versionchanged:: 3.5
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|       Affects comparisons of :class:`bytes` with :class:`int`.
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| 
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| .. cmdoption:: -B
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| 
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|    If given, Python won't try to write ``.pyc`` files on the
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|    import of source modules.  See also :envvar:`PYTHONDONTWRITEBYTECODE`.
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| 
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| 
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| .. cmdoption:: -d
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| 
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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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| 
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| 
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| .. cmdoption:: -E
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| 
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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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| 
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| 
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| .. cmdoption:: -i
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| 
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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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| 
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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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| 
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| 
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| .. cmdoption:: -I
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| 
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|    Run Python in isolated mode. This also implies -E and -s.
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|    In isolated mode :data:`sys.path` contains neither the script's directory nor
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|    the user's site-packages directory. All :envvar:`PYTHON*` environment
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|    variables are ignored, too. Further restrictions may be imposed to prevent
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|    the user from injecting malicious code.
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| 
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|    .. versionadded:: 3.4
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| 
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| 
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| .. cmdoption:: -O
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| 
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|    Turn on basic optimizations.  See also :envvar:`PYTHONOPTIMIZE`.
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| 
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| 
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| .. cmdoption:: -OO
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| 
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|    Discard docstrings in addition to the :option:`-O` optimizations.
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| 
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| 
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| .. cmdoption:: -q
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| 
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|    Don't display the copyright and version messages even in interactive mode.
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| 
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|    .. versionadded:: 3.2
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| 
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| 
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| .. cmdoption:: -R
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| 
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|    Kept for compatibility.  On Python 3.3 and greater, hash randomization is
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|    turned on by default.
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| 
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|    On previous versions of Python, this option turns on hash randomization,
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|    so that the :meth:`__hash__` values of str, bytes and datetime
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|    are "salted" with an unpredictable random value.  Although they remain
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|    constant within an individual Python process, they are not predictable
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|    between repeated invocations of Python.
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| 
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|    Hash randomization is intended to provide protection against a
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|    denial-of-service caused by carefully-chosen inputs that exploit the worst
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|    case performance of a dict construction, O(n^2) complexity.  See
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|    http://www.ocert.org/advisories/ocert-2011-003.html for details.
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| 
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|    :envvar:`PYTHONHASHSEED` allows you to set a fixed value for the hash
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|    seed secret.
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| 
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|    .. versionadded:: 3.2.3
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| 
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| 
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| .. cmdoption:: -s
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| 
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|    Don't add the :data:`user site-packages directory <site.USER_SITE>` to
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|    :data:`sys.path`.
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| 
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|    .. seealso::
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| 
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|       :pep:`370` -- Per user site-packages directory
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| 
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| 
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| .. cmdoption:: -S
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| 
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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.  Also disable these
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|    manipulations if :mod:`site` is explicitly imported later (call
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|    :func:`site.main` if you want them to be triggered).
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| 
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| 
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| .. cmdoption:: -u
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| 
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|    Force the binary layer of the stdout and stderr streams (which is
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|    available as their ``buffer`` attribute) to be unbuffered. The text I/O
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|    layer will still be line-buffered if writing to the console, or
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|    block-buffered if redirected to a non-interactive file.
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| 
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|    See also :envvar:`PYTHONUNBUFFERED`.
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| 
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| 
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| .. cmdoption:: -v
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| 
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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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| 
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| 
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| .. _using-on-warnings:
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| .. cmdoption:: -W arg
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| 
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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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| 
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|        file:line: category: message
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| 
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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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| 
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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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| 
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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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| 
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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 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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| 
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|        action:message:category:module:line
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| 
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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 tests 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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| 
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|    .. seealso::
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|       :mod:`warnings` -- the warnings module
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| 
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|       :pep:`230` -- Warning framework
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| 
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|       :envvar:`PYTHONWARNINGS`
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| 
 | |
| 
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| .. cmdoption:: -x
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| 
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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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| 
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|    .. note:: The line numbers in error messages will be off by one.
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| 
 | |
| 
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| .. cmdoption:: -X
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| 
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|    Reserved for various implementation-specific options.  CPython currently
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|    defines the following possible values:
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| 
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|    * ``-X faulthandler`` to enable :mod:`faulthandler`;
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|    * ``-X showrefcount`` to enable the output of the total reference count
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|      and memory blocks (only works on debug builds);
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|    * ``-X tracemalloc`` to start tracing Python memory allocations using the
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|      :mod:`tracemalloc` module. By default, only the most recent frame is
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|      stored in a traceback of a trace. Use ``-X tracemalloc=NFRAME`` to start
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|      tracing with a traceback limit of *NFRAME* frames. See the
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|      :func:`tracemalloc.start` for more information.
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| 
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|    It also allows passing arbitrary values and retrieving them through the
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|    :data:`sys._xoptions` dictionary.
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| 
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|    .. versionchanged:: 3.2
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|       It is now allowed to pass :option:`-X` with CPython.
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| 
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|    .. versionadded:: 3.3
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|       The ``-X faulthandler`` option.
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| 
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|    .. versionadded:: 3.4
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|       The ``-X showrefcount`` and ``-X tracemalloc`` options.
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| 
 | |
| 
 | |
| Options you shouldn't use
 | |
| ~~~~~~~~~~~~~~~~~~~~~~~~~
 | |
| 
 | |
| .. cmdoption:: -J
 | |
| 
 | |
|    Reserved for use by Jython_.
 | |
| 
 | |
| .. _Jython: http://www.jython.org/
 | |
| 
 | |
| 
 | |
| .. _using-on-envvars:
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| 
 | |
| Environment variables
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| ---------------------
 | |
| 
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| These environment variables influence Python's behavior, they are processed
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| before the command-line switches other than -E or -I.  It is customary that
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| command-line switches override environmental variables where there is a
 | |
| conflict.
 | |
| 
 | |
| .. envvar:: PYTHONHOME
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| 
 | |
|    Change the location of the standard Python libraries.  By default, the
 | |
|    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`.
 | |
| 
 | |
|    When :envvar:`PYTHONHOME` is set to a single directory, its value replaces
 | |
|    both :file:`{prefix}` and :file:`{exec_prefix}`.  To specify different values
 | |
|    for these, set :envvar:`PYTHONHOME` to :file:`{prefix}:{exec_prefix}`.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONPATH
 | |
| 
 | |
|    Augment the default search path for module files.  The format is the same as
 | |
|    the shell's :envvar:`PATH`: one or more directory pathnames separated by
 | |
|    :data:`os.pathsep` (e.g. colons on Unix or semicolons on Windows).
 | |
|    Non-existent directories are silently ignored.
 | |
| 
 | |
|    In addition to normal directories, individual :envvar:`PYTHONPATH` entries
 | |
|    may refer to zipfiles containing pure Python modules (in either source or
 | |
|    compiled form). Extension modules cannot be imported from zipfiles.
 | |
| 
 | |
|    The default search path is installation dependent, but generally begins with
 | |
|    :file:`{prefix}/lib/python{version}` (see :envvar:`PYTHONHOME` above).  It
 | |
|    is *always* appended to :envvar:`PYTHONPATH`.
 | |
| 
 | |
|    An additional directory will be inserted in the search path in front of
 | |
|    :envvar:`PYTHONPATH` as described above under
 | |
|    :ref:`using-on-interface-options`. The search path can be manipulated from
 | |
|    within a Python program as the variable :data:`sys.path`.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONSTARTUP
 | |
| 
 | |
|    If this is the name of a readable file, the Python commands in that file are
 | |
|    executed before the first prompt is displayed in interactive mode.  The file
 | |
|    is executed in the same namespace where interactive commands are executed so
 | |
|    that objects defined or imported in it can be used without qualification in
 | |
|    the interactive session.  You can also change the prompts :data:`sys.ps1` and
 | |
|    :data:`sys.ps2` and the hook :data:`sys.__interactivehook__` in this file.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONOPTIMIZE
 | |
| 
 | |
|    If this is set to a non-empty string it is equivalent to specifying the
 | |
|    :option:`-O` option.  If set to an integer, it is equivalent to specifying
 | |
|    :option:`-O` multiple times.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONDEBUG
 | |
| 
 | |
|    If this is set to a non-empty string it is equivalent to specifying the
 | |
|    :option:`-d` option.  If set to an integer, it is equivalent to specifying
 | |
|    :option:`-d` multiple times.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONINSPECT
 | |
| 
 | |
|    If this is set to a non-empty string it is equivalent to specifying the
 | |
|    :option:`-i` option.
 | |
| 
 | |
|    This variable can also be modified by Python code using :data:`os.environ`
 | |
|    to force inspect mode on program termination.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONUNBUFFERED
 | |
| 
 | |
|    If this is set to a non-empty string it is equivalent to specifying the
 | |
|    :option:`-u` option.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONVERBOSE
 | |
| 
 | |
|    If this is set to a non-empty string it is equivalent to specifying the
 | |
|    :option:`-v` option.  If set to an integer, it is equivalent to specifying
 | |
|    :option:`-v` multiple times.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONCASEOK
 | |
| 
 | |
|    If this is set, Python ignores case in :keyword:`import` statements.  This
 | |
|    only works on Windows and OS X.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONDONTWRITEBYTECODE
 | |
| 
 | |
|    If this is set to a non-empty string, Python won't try to write ``.pyc`` or
 | |
|    ``.pyo`` files on the import of source modules.  This is equivalent to
 | |
|    specifying the :option:`-B` option.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONHASHSEED
 | |
| 
 | |
|    If this variable is not set or set to ``random``, a random value is used
 | |
|    to seed the hashes of str, bytes and datetime objects.
 | |
| 
 | |
|    If :envvar:`PYTHONHASHSEED` is set to an integer value, it is used as a fixed
 | |
|    seed for generating the hash() of the types covered by the hash
 | |
|    randomization.
 | |
| 
 | |
|    Its purpose is to allow repeatable hashing, such as for selftests for the
 | |
|    interpreter itself, or to allow a cluster of python processes to share hash
 | |
|    values.
 | |
| 
 | |
|    The integer must be a decimal number in the range [0,4294967295].  Specifying
 | |
|    the value 0 will disable hash randomization.
 | |
| 
 | |
|    .. versionadded:: 3.2.3
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONIOENCODING
 | |
| 
 | |
|    If this is set before running the interpreter, it overrides the encoding used
 | |
|    for stdin/stdout/stderr, in the syntax ``encodingname:errorhandler``.  Both
 | |
|    the ``encodingname`` and the ``:errorhandler`` parts are optional and have
 | |
|    the same meaning as in :func:`str.encode`.
 | |
| 
 | |
|    For stderr, the ``:errorhandler`` part is ignored; the handler will always be
 | |
|    ``'backslashreplace'``.
 | |
| 
 | |
|    .. versionchanged:: 3.4
 | |
|       The ``encodingname`` part is now optional.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONNOUSERSITE
 | |
| 
 | |
|    If this is set, Python won't add the :data:`user site-packages directory
 | |
|    <site.USER_SITE>` to :data:`sys.path`.
 | |
| 
 | |
|    .. seealso::
 | |
| 
 | |
|       :pep:`370` -- Per user site-packages directory
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONUSERBASE
 | |
| 
 | |
|    Defines the :data:`user base directory <site.USER_BASE>`, which is used to
 | |
|    compute the path of the :data:`user site-packages directory <site.USER_SITE>`
 | |
|    and :ref:`Distutils installation paths <inst-alt-install-user>` for
 | |
|    ``python setup.py install --user``.
 | |
| 
 | |
|    .. seealso::
 | |
| 
 | |
|       :pep:`370` -- Per user site-packages directory
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONEXECUTABLE
 | |
| 
 | |
|    If this environment variable is set, ``sys.argv[0]`` will be set to its
 | |
|    value instead of the value got through the C runtime.  Only works on
 | |
|    Mac OS X.
 | |
| 
 | |
| .. envvar:: PYTHONWARNINGS
 | |
| 
 | |
|    This is equivalent to the :option:`-W` option. If set to a comma
 | |
|    separated string, it is equivalent to specifying :option:`-W` multiple
 | |
|    times.
 | |
| 
 | |
| .. envvar:: PYTHONFAULTHANDLER
 | |
| 
 | |
|    If this environment variable is set to a non-empty string,
 | |
|    :func:`faulthandler.enable` is called at startup: install a handler for
 | |
|    :const:`SIGSEGV`, :const:`SIGFPE`, :const:`SIGABRT`, :const:`SIGBUS` and
 | |
|    :const:`SIGILL` signals to dump the Python traceback.  This is equivalent to
 | |
|    :option:`-X` ``faulthandler`` option.
 | |
| 
 | |
|    .. versionadded:: 3.3
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONTRACEMALLOC
 | |
| 
 | |
|    If this environment variable is set to a non-empty string, start tracing
 | |
|    Python memory allocations using the :mod:`tracemalloc` module. The value of
 | |
|    the variable is the maximum number of frames stored in a traceback of a
 | |
|    trace. For example, ``PYTHONTRACEMALLOC=1`` stores only the most recent
 | |
|    frame. See the :func:`tracemalloc.start` for more information.
 | |
| 
 | |
|    .. versionadded:: 3.4
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONASYNCIODEBUG
 | |
| 
 | |
|    If this environment variable is set to a non-empty string, enable the
 | |
|    :ref:`debug mode <asyncio-debug-mode>` of the :mod:`asyncio` module.
 | |
| 
 | |
|    .. versionadded:: 3.4
 | |
| 
 | |
| 
 | |
| Debug-mode variables
 | |
| ~~~~~~~~~~~~~~~~~~~~
 | |
| 
 | |
| Setting these variables only has an effect in a debug build of Python, that is,
 | |
| if Python was configured with the ``--with-pydebug`` build option.
 | |
| 
 | |
| .. envvar:: PYTHONTHREADDEBUG
 | |
| 
 | |
|    If set, Python will print threading debug info.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONDUMPREFS
 | |
| 
 | |
|    If set, Python will dump objects and reference counts still alive after
 | |
|    shutting down the interpreter.
 | |
| 
 | |
| 
 | |
| .. envvar:: PYTHONMALLOCSTATS
 | |
| 
 | |
|    If set, Python will print memory allocation statistics every time a new
 | |
|    object arena is created, and on shutdown.
 |