PYTHON(1)                   General Commands Manual                  PYTHON(1)

       python  - an interpreted, interactive, object-oriented programming lan-

       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 ]

       Python is an interpreted, interactive, object-oriented programming lan-
       guage  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, con-
       stants, 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 RE-
       SOURCES 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 applica-
       tions.  See the internal documentation for hints.

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

       -B     Don't  write .pyc files on import. See also PYTHONDONTWRITEBYTE-

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

       -c command
              Specify the command to execute (see next section).  This  termi-
              nates 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 correspond-
              ing .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  com-
              piled  (bytecode)  files by adding .opt-2 before the .pyc exten-

       -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 ma-
              nipulations of sys.path that it entails.  Also disable these ma-
              nipulations if site is explicitly imported later.

       -u     Force  the stdout and stderr streams to be unbuffered.  This op-
              tion 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  mod-

              The  simplest  form  of  argument is one of the following action
              strings (or a unique abbreviation): ignore to ignore  all  warn-
              ings; default to explicitly request the default behavior (print-
              ing each warning once per source line); all to print  a  warning
              each  time it occurs (this may generate many messages if a warn-
              ing 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 excep-
              tion instead of printing a warning message.

              The  full  form  of  argument  is   action:message:category:mod-
              ule: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 warn-
              ing 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  num-
              ber,  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

                  -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 us-
              ing 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  ob-
              jects 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
                      nested imports). Note that its output may be  broken  in
                      application.  Typical  usage is python3 -X importtime -c
              'import asyncio'

                  -X dev: enable CPython's "development mode", introducing ad-
              ditional 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 par-
              allel 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!

       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 multi-
       ple statements separated by newlines.  Leading whitespace  is  signifi-
       cant  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 ex-
       ception; other UNIX signals are not  caught  (except  that  SIGPIPE  is
       sometimes  ignored, in favor of the IOError exception).  Error messages
       are written to stderr.

       These are subject to difference depending on local installation conven-
       tions;  ${prefix}  and  ${exec_prefix}  are  installation-dependent and
       should be interpreted as for GNU software; they may be  the  same.   On
       Debian GNU/{Hurd,Linux} the default for both is /usr.

              Recommended location of the interpreter.

              Recommended locations of the directories containing the standard

              Recommended locations of the directories containing the  include
              files  needed for developing Python extensions and embedding the

              Change the location of the standard Python  libraries.   By  de-
              fault,  the  libraries are searched in ${prefix}/lib/python<ver-
              sion> 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 ${pre-

              Augments  the  default search path for module files.  The format
              is the same as the shell's $PATH: one or  more  directory  path-
              names   separated   by  colons.   Non-existent  directories  are
              silently ignored.  The default search path is  installation  de-
              pendent, but generally begins with ${prefix}/lib/python<version>
              (see PYTHONHOME above).  The default search path is  always  ap-
              pended  to  $PYTHONPATH.  If a script argument is given, the di-
              rectory 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.

              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  in-
              teractive  session.  You can also change the prompts sys.ps1 and
              sys.ps2 in this file.

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

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

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

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

              If this is set before running the interpreter, it overrides  the
              encoding  used  for stdin/stdout/stderr, in the syntax encoding-
              name: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'.

              If  this is set to a non-empty string it is equivalent to speci-
              fying the -s option  (Don't  add  the  user  site  directory  to

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

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

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

              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 ran-

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

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

              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  vari-
              able  is used to force the malloc(3) allocator of the C library,
              or if Python is configured without pymalloc support.

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

              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.

              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.

              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.

              Defines  the  user  base directory, which is used to compute the
              path of the user site-packages directory and Distutils installa-
              tion paths for python install --user.

              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.

              If  this  environment  variable is set to 0, it disables the de-
              fault 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.

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

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

       The Python Software Foundation:

       Main website:
       Developer resources:
       Module repository:
       Newsgroups:  comp.lang.python, comp.lang.python.announce

       Python  is distributed under an Open Source license.  See the file "LI-
       CENSE" in the Python source distribution for  information  on  terms  &
       conditions  for  accessing  and  otherwise  using Python and for a DIS-

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