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 PYTHON(1)                                                         PYTHON(1)




 NAME
      python - an interpreted, interactive, object-oriented programming
      language

 SYNOPSIS
      python [ -B ] [ -b ] [ -d ] [ -E ] [ -h ] [ -i ] [ -I ]
             [ -m module-name ] [ -q ] [ -O ] [ -OO ] [ -s ] [ -S ] [ -u ]
             [ -v ] [ -V ] [ -W argument ] [ -x ] [ [ -X option ] -? ]
             [ --check-hash-based-pycs default | always | never ]
             [ -c command | script | - ] [ arguments ]

 DESCRIPTION
      Python is an interpreted, interactive, object-oriented programming
      language that combines remarkable power with very clear syntax.  For
      an introduction to programming in Python, see the Python Tutorial.
      The Python Library Reference documents built-in and standard types,
      constants, functions and modules.  Finally, the Python Reference
      Manual describes the syntax and semantics of the core language in
      (perhaps too) much detail.  (These documents may be located via the
      INTERNET RESOURCES below; they may be installed on your system as
      well.)

      Python's basic power can be extended with your own modules written in
      C or C++.  On most systems such modules may be dynamically loaded.
      Python is also adaptable as an extension language for existing
      applications.  See the internal documentation for hints.

      Documentation for installed Python modules and packages can be viewed
      by running the pydoc program.

 COMMAND LINE OPTIONS
      -B   Don't write .pyc files on import. See also
           PYTHONDONTWRITEBYTECODE.

      -b   Issue warnings about str(bytes_instance), str(bytearray_instance)
           and comparing bytes/bytearray with str. (-bb: issue errors)

      -c command
           Specify the command to execute (see next section).  This
           terminates the option list (following options are passed as
           arguments to the command).

      --check-hash-based-pycs mode
           Configure how Python evaluates the up-to-dateness of hash-based
           .pyc files.

      -d   Turn on parser debugging output (for expert only, depending on
           compilation options).

      -E   Ignore environment variables like PYTHONPATH and PYTHONHOME that
           modify the behavior of the interpreter.



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 PYTHON(1)                                                         PYTHON(1)




      -h ,  -? ,  --help
           Prints the usage for the interpreter executable and exits.

      -i   When a script is passed as first argument or the -c option is
           used, enter interactive mode after executing the script or the
           command.  It does not read the $PYTHONSTARTUP file.  This can be
           useful to inspect global variables or a stack trace when a script
           raises an exception.

      -I   Run Python in isolated mode. This also implies -E and -s. In
           isolated mode sys.path contains neither the script's directory
           nor the user's site-packages directory. All PYTHON* environment
           variables are ignored, too.  Further restrictions may be imposed
           to prevent the user from injecting malicious code.

      -m module-name
           Searches sys.path for the named module and runs the corresponding
           .py file as a script.

      -O   Remove assert statements and any code conditional on the value of
           __debug__; augment the filename for compiled (bytecode) files by
           adding .opt-1 before the .pyc extension.

      -OO  Do -O and also discard docstrings; change the filename for
           compiled (bytecode) files by adding .opt-2 before the .pyc
           extension.

      -q   Do not print the version and copyright messages. These messages
           are also suppressed in non-interactive mode.

      -s   Don't add user site directory to sys.path.

      -S   Disable the import of the module site and the site-dependent
           manipulations of sys.path that it entails.  Also disable these
           manipulations if site is explicitly imported later.

      -u   Force the stdout and stderr streams to be unbuffered.  This
           option has no effect on the stdin stream.

      -v   Print a message each time a module is initialized, showing the
           place (filename or built-in module) from which it is loaded.
           When given twice, print a message for each file that is checked
           for when searching for a module.  Also provides information on
           module cleanup at exit.

      -V ,  --version
           Prints the Python version number of the executable and exits.
           When given twice, print more information about the build.

      -W argument
           Warning control.  Python sometimes prints warning message to



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 PYTHON(1)                                                         PYTHON(1)




           sys.stderr.  A typical warning message has the following form:
           file:line: category: By default, each warning is printed once for
           each source line where it occurs.  This option controls how often
           warnings are printed.  Multiple -W options may be given; when a
           warning matches more than one option, the action for the last
           matching option is performed.  Invalid -W options are ignored (a
           warning message is printed about invalid options when the first
           warning is issued).  Warnings can also be controlled from within
           a Python program using the warnings module.

           The simplest form of argument is one of the following action
           strings (or a unique abbreviation): ignore to ignore all
           warnings; default to explicitly request the default behavior
           (printing each warning once per source line); all to print a
           warning each time it occurs (this may generate many messages if a
           warning is triggered repeatedly for the same source line, such as
           inside a loop); module to print each warning only the first time
           it occurs in each module; once to print each warning only the
           first time it occurs in the program; or error to raise an
           exception instead of printing a warning message.

           The full form of argument is action:message:category: Here,
           action is as explained above but only applies to messages that
           match the remaining fields.  Empty fields match all values;
           trailing empty fields may be omitted.  The message field matches
           the start of the warning message printed; this match is case-
           insensitive.  The category field matches the warning category.
           This must be a class name; the match test whether the actual
           warning category of the message is a subclass of the specified
           warning category.  The full class name must be given.  The module
           field matches the (fully-qualified) module name; this match is
           case-sensitive.  The line field matches the line number, where
           zero matches all line numbers and is thus equivalent to an
           omitted line number.

      -X option
           Set implementation specific option. The following options are
           available:

               -X faulthandler: enable faulthandler

               -X showrefcount: output the total reference count and number
           of used
                   memory blocks when the program finishes or after each
           statement in the
                   interactive interpreter. This only works on debug builds

               -X tracemalloc: start tracing Python memory allocations using
           the
                   tracemalloc module. By default, only the most recent
           frame is stored in a



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 PYTHON(1)                                                         PYTHON(1)




                   traceback of a trace. Use -X tracemalloc=NFRAME to start
           tracing with a
                   traceback limit of NFRAME frames

               -X importtime: show how long each import takes. It shows
           module name,
                   cumulative time (including nested imports) and self time
           (excluding
                   nested imports). Note that its output may be broken in
           multi-threaded
                   application. Typical usage is python3 -X importtime -c
           'import asyncio'

               -X dev: enable CPython's "development mode", introducing
           additional runtime
                   checks which are too expensive to be enabled by default.
           It will not be
                   more verbose than the default if the code is correct: new
           warnings are
                   only emitted when an issue is detected. Effect of the
           developer mode:
                      * Add default warning filter, as -W default
                      * Install debug hooks on memory allocators: see the
           PyMem_SetupDebugHooks() C function
                      * Enable the faulthandler module to dump the Python
           traceback on a crash
                      * Enable asyncio debug mode
                      * Set the dev_mode attribute of sys.flags to True
                      * io.IOBase destructor logs close() exceptions

               -X utf8: enable UTF-8 mode for operating system interfaces,
           overriding the default
                   locale-aware mode. -X utf8=0 explicitly disables UTF-8
           mode (even when it would
                   otherwise activate automatically). See PYTHONUTF8 for
           more details

               -X pycache_prefix=PATH: enable writing .pyc files to a
           parallel tree rooted at the
                    given directory instead of to the code tree.

      -x   Skip the first line of the source.  This is intended for a DOS
           specific hack only.  Warning: the line numbers in error messages
           will be off by one!

 INTERPRETER INTERFACE
      The interpreter interface resembles that of the UNIX shell: when
      called with standard input connected to a tty device, it prompts for
      commands and executes them until an EOF is read; when called with a
      file name argument or with a file as standard input, it reads and
      executes a script from that file; when called with -c command, it



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 PYTHON(1)                                                         PYTHON(1)




      executes the Python statement(s) given as command.  Here command may
      contain multiple statements separated by newlines.  Leading whitespace
      is significant in Python statements!  In non-interactive mode, the
      entire input is parsed before it is executed.

      If available, the script name and additional arguments thereafter are
      passed to the script in the Python variable sys.argv, which is a list
      of strings (you must first import sys to be able to access it).  If no
      script name is given, sys.argv[0] is an empty string; if -c is used,
      sys.argv[0] contains the string '-c'. Note that options interpreted by
      the Python interpreter itself are not placed in sys.argv.

      In interactive mode, the primary prompt is `>>>'; the second prompt
      (which appears when a command is not complete) is `...'.  The prompts
      can be changed by assignment to sys.ps1 or sys.ps2.  The interpreter
      quits when it reads an EOF at a prompt.  When an unhandled exception
      occurs, a stack trace is printed and control returns to the primary
      prompt; in non-interactive mode, the interpreter exits after printing
      the stack trace.  The interrupt signal raises the KeyboardInterrupt
      exception; other UNIX signals are not caught (except that SIGPIPE is
      sometimes ignored, in favor of the IOError exception).  Error messages
      are written to stderr.

 FILES AND DIRECTORIES
      These are subject to difference depending on local installation
      conventions; ${prefix} and ${exec_prefix} are installation-dependent
      and should be interpreted as for GNU software; they may be the same.
      The default for both is /usr/local.

      ${exec_prefix}/bin/python
           Recommended location of the interpreter.

      ${prefix}/lib/python<version>
      ${exec_prefix}/lib/python<version>
           Recommended locations of the directories containing the standard
           modules.

      ${prefix}/include/python<version>
      ${exec_prefix}/include/python<version>
           Recommended locations of the directories containing the include
           files needed for developing Python extensions and embedding the
           interpreter.

 ENVIRONMENT VARIABLES
      PYTHONHOME
           Change the location of the standard Python libraries.  By
           default, the libraries are searched in
           ${prefix}/lib/python<version> and
           ${exec_prefix}/lib/python<version>, where ${prefix} and
           ${exec_prefix} are installation-dependent directories, both
           defaulting to /usr/local.  When $PYTHONHOME is set to a single



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 PYTHON(1)                                                         PYTHON(1)




           directory, its value replaces both ${prefix} and ${exec_prefix}.
           To specify different values for these, set $PYTHONHOME to
           ${prefix}:${exec_prefix}.

      PYTHONPATH
           Augments the default search path for module files.  The format is
           the same as the shell's $PATH: one or more directory pathnames
           separated by colons.  Non-existent directories are silently
           ignored.  The default search path is installation dependent, but
           generally begins with ${prefix}/lib/python<version> (see
           PYTHONHOME above).  The default search path is always appended to
           $PYTHONPATH.  If a script argument is given, the directory
           containing the script is inserted in the path in front of
           $PYTHONPATH.  The search path can be manipulated from within a
           Python program as the variable sys.path.

      PYTHONPLATLIBDIR
           Override sys.platlibdir.

      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 name space
           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 sys.ps1 and
           sys.ps2 in this file.

      PYTHONOPTIMIZE
           If this is set to a non-empty string it is equivalent to
           specifying the -O option. If set to an integer, it is equivalent
           to specifying -O multiple times.

      PYTHONDEBUG
           If this is set to a non-empty string it is equivalent to
           specifying the -d option. If set to an integer, it is equivalent
           to specifying -d multiple times.

      PYTHONDONTWRITEBYTECODE
           If this is set to a non-empty string it is equivalent to
           specifying the -B option (don't try to write .pyc files).

      PYTHONINSPECT
           If this is set to a non-empty string it is equivalent to
           specifying the -i option.

      PYTHONIOENCODING
           If this is set before running the interpreter, it overrides the
           encoding used for stdin/stdout/stderr, in the syntax
           encodingname:errorhandler The errorhandler part is optional and
           has the same meaning as in str.encode. For stderr, the



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 PYTHON(1)                                                         PYTHON(1)




           errorhandler
            part is ignored; the handler will always be 'backslashreplace'.

      PYTHONNOUSERSITE
           If this is set to a non-empty string it is equivalent to
           specifying the -s option (Don't add the user site directory to
           sys.path).

      PYTHONUNBUFFERED
           If this is set to a non-empty string it is equivalent to
           specifying the -u option.

      PYTHONVERBOSE
           If this is set to a non-empty string it is equivalent to
           specifying the -v option. If set to an integer, it is equivalent
           to specifying -v multiple times.

      PYTHONWARNINGS
           If this is set to a comma-separated string it is equivalent to
           specifying the -W option for each separate value.

      PYTHONHASHSEED
           If this variable is set to "random", a random value is used to
           seed the hashes of str and bytes objects.

           If 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.

      PYTHONMALLOC
           Set the Python memory allocators and/or install debug hooks. The
           available memory allocators are malloc and pymalloc.  The
           available debug hooks are debug, malloc_debug, and
           pymalloc_debug.

           When Python is compiled in debug mode, the default is
           pymalloc_debug and the debug hooks are automatically used.
           Otherwise, the default is pymalloc.

      PYTHONMALLOCSTATS
           If set to a non-empty string, Python will print statistics of the
           pymalloc memory allocator every time a new pymalloc object arena
           is created, and on shutdown.

           This variable is ignored if the $PYTHONMALLOC environment
           variable is used to force the malloc(3) allocator of the C



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 PYTHON(1)                                                         PYTHON(1)




           library, or if Python is configured without pymalloc support.

      PYTHONASYNCIODEBUG
           If this environment variable is set to a non-empty string, enable
           the debug mode of the asyncio module.

      PYTHONTRACEMALLOC
           If this environment variable is set to a non-empty string, start
           tracing Python memory allocations using the 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.

      PYTHONFAULTHANDLER
           If this environment variable is set to a non-empty string,
           faulthandler.enable() is called at startup: install a handler for
           SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL signals to dump the
           Python traceback.

           This is equivalent to the -X faulthandler option.

      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.

      PYTHONUSERBASE
           Defines the user base directory, which is used to compute the
           path of the user site-packages directory and Distutils
           installation paths for python setup.py install --user.

      PYTHONPROFILEIMPORTTIME
           If this environment variable is set to a non-empty string, Python
           will show how long each import takes. This is exactly equivalent
           to setting -X importtime on the command line.

      PYTHONBREAKPOINT
           If this environment variable is set to 0, it disables the default
           debugger. It can be set to the callable of your debugger of
           choice.

    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.

      PYTHONTHREADDEBUG
           If this environment variable is set, Python will print threading
           debug info.




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 PYTHON(1)                                                         PYTHON(1)




      PYTHONDUMPREFS
           If this environment variable is set, Python will dump objects and
           reference counts still alive after shutting down the interpreter.

 AUTHOR
      The Python Software Foundation: https://www.python.org/psf/

 INTERNET RESOURCES
      Main website:  https://www.python.org/
      Documentation:  https://docs.python.org/
      Developer resources:  https://devguide.python.org/
      Downloads:  https://www.python.org/downloads/
      Module repository:  https://pypi.org/
      Newsgroups:  comp.lang.python, comp.lang.python.announce

 LICENSING
      Python is distributed under an Open Source license.  See the file
      "LICENSE" in the Python source distribution for information on terms &
      conditions for accessing and otherwise using Python and for a
      DISCLAIMER OF ALL WARRANTIES.


































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