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 ] [ -P ] [ -s ] [ -S ] [ -u ]
              [ -v ] [ -V ] [ -W argument ] [ -x ] [ -X option ] [ -?  ]
              [ --check-hash-based-pycs default | always | never ]
              [ --help ] [ --help-env ] [ --help-xoptions ] [ --help-all ]
              [ -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.

       --help-env
              Prints help about Python-specific environment variables and exits.

       --help-xoptions
              Prints help about implementation-specific -X options and exits.

       --help-all
              Prints complete usage information 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, -P and -s. In isolated mode
              sys.path contains neither the script's directory nor the user's site-packages  direc‐
              tory.  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. This terminates the option list (following options are passed as arguments to
              the module).

       -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  exten‐
              sion.

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

       -P     Don't automatically prepend a potentially unsafe path to sys.path such as the current
              directory, the script's directory or an empty string. See also the PYTHONSAFEPATH en‐
              vironment variable.

       -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 im‐
              ported 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's warning machinery by default  prints  warning  messages  to
              sys.stderr.

              The simplest settings apply a particular action unconditionally to all warnings emit‐
              ted by a process (even those that are otherwise ignored by default):

                -Wdefault  # Warn once per call location
                -Werror    # Convert to exceptions
                -Walways   # Warn every time
                -Wall      # Same as -Walways
                -Wmodule   # Warn once per calling module
                -Wonce     # Warn once per Python process
                -Wignore   # Never warn

              The  action names can be abbreviated as desired and the interpreter will resolve them
              to the appropriate action name. For example, -Wi is the same as -Wignore .

              The full form of argument is: action:message:category:module:lineno

              Empty fields match all values; trailing empty fields may be omitted. For  example  -W
              ignore::DeprecationWarning ignores all DeprecationWarning warnings.

              The  action  field  is as explained above but only applies to warnings that match the
              remaining fields.

              The message field must match the whole printed warning message; this match  is  case-
              insensitive.

              The category field matches the warning category (ex: "DeprecationWarning"). 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 module field matches the (fully-qualified) module name; this match is case-sensi‐
              tive.

              The  lineno field matches the line number, where zero matches all line numbers and is
              thus equivalent to an omitted line number.

              Multiple -W options can be given; when a warning matches more than  one  option,  the
              action  for  the  last  matching  option is performed. Invalid -W options are ignored
              (though, a warning message is printed about invalid options when the first warning is
              issued).

              Warnings can also be controlled using the  PYTHONWARNINGS  environment  variable  and
              from  within  a  Python  program  using  the warnings module.  For example, the warn‐
              ings.filterwarnings() function can be used to use a regular expression on the warning
              message.

       -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 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_SetupDe‐
              bugHooks()
                           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 de‐
              fault
                      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 warn_default_encoding: enable opt-in EncodingWarning for 'encoding=None'

                  -X no_debug_ranges: disable the inclusion of the tables mapping extra location
                     information (end line, start column offset and end column offset) to every
                     instruction in code objects. This is useful when smaller code objects and pyc
                     files are desired as well as suppressing the extra visual location indicators
                     when the interpreter displays tracebacks.

                  -X frozen_modules=[on|off]: whether or not frozen modules should be used.
                     The default is "on" (or "off" if you are running a local build).

                  -X int_max_str_digits=number: limit the size of int<->str conversions.
                     This helps avoid denial of service attacks when parsing untrusted data.
                     The default is sys.int_info.default_max_str_digits.  0 disables.

       -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 exe‐
       cutes a script from that file; when called with -c command, it executes  the  Python  state‐
       ment(s)  given  as  command.  Here command may contain multiple statements separated by new‐
       lines.  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 in‐
       terpreter 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 excep‐
       tion occurs, a stack trace is printed and control returns to the primary prompt; in  non-in‐
       teractive  mode, the interpreter exits after printing the stack trace.  The interrupt signal
       raises the KeyboardInterrupt exception; other UNIX signals are not caught (except that  SIG‐
       PIPE  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  de‐
              veloping Python extensions and embedding the interpreter.

ENVIRONMENT VARIABLES
       PYTHONSAFEPATH
              If  this  is set to a non-empty string, don't automatically prepend a potentially un‐
              safe path to sys.path such as the current directory, the  script's  directory  or  an
              empty string. See also the -P option.

       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 de‐
              faulting to /usr/local.  When $PYTHONHOME is set to a single directory, its value re‐
              places 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 di‐
              rectories  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 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  op‐
              tion 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 generat‐
              ing the hash() of the types covered by the hash randomization.  Its purpose is to al‐
              low 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.

       PYTHONINTMAXSTRDIGITS
              Limit the maximum digit characters in an int value when converting from a string  and
              when  converting an int back to a str.  A value of 0 disables the limit.  Conversions
              to or from bases 2, 4, 8, 16, and 32 are never limited.

       PYTHONMALLOC
              Set the Python memory allocators and/or install debug hooks. The available memory al‐
              locators 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 al‐
              locator 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 mem‐
              ory 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 installation paths for python -m pip 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.

       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)
