python

PYTHON(1)                   General Commands Manual                  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.

       -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
              sys.stderr.  A typical warning message has the following form:
              file:line: category: message.  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:module:line.  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
                      traceback of a trace. Use -X tracemalloc=NFRAME to start
              tracing with a
                      traceback limit of NFRAME frames

                  -X showalloccount: output the total count of allocated
              objects for each
                      type when the program finishes. This only works when
              Python was built with
                      COUNT_ALLOCS defined

                  -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 CPythonâs âdevelopment modeâ, 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 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
              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.

       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
              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
              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.

       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.



                                                                     PYTHON(1)