1PYTHON(1)                   General Commands Manual                  PYTHON(1)
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NAME

6       python  - an interpreted, interactive, object-oriented programming lan‐
7       guage
8

SYNOPSIS

10       python [ -B ] [ -d ] [ -E ] [ -h ] [ -i ] [ -m module-name ]
11              [ -O ] [ -OO ] [ -R ] [ -Q argument ] [ -s ] [ -S ] [ -t ] [  -u
12       ]
13              [ -v ] [ -V ] [ -W argument ] [ -x ] [ -3 ] [ -?  ]
14              [ -c command | script | - ] [ arguments ]
15

DESCRIPTION

17       Python is an interpreted, interactive, object-oriented programming lan‐
18       guage that combines remarkable power with very clear  syntax.   For  an
19       introduction  to  programming  in Python, see the Python Tutorial.  The
20       Python Library Reference documents built-in and  standard  types,  con‐
21       stants,  functions  and  modules.  Finally, the Python Reference Manual
22       describes the syntax and semantics of the  core  language  in  (perhaps
23       too)  much  detail.   (These  documents may be located via the INTERNET
24       RESOURCES below; they may be installed on your system as well.)
25
26       Python's basic power can be extended with your own modules written in C
27       or  C++.   On  most  systems  such  modules  may be dynamically loaded.
28       Python is also adaptable as an extension language for existing applica‐
29       tions.  See the internal documentation for hints.
30
31       Documentation  for  installed Python modules and packages can be viewed
32       by running the pydoc program.
33

COMMAND LINE OPTIONS

35       -B     Don't write .py[co] files on import. See  also  PYTHONDONTWRITE‐
36              BYTECODE.
37
38       -c command
39              Specify  the command to execute (see next section).  This termi‐
40              nates the option list (following options are passed as arguments
41              to the command).
42
43       -d     Turn  on parser debugging output (for wizards only, depending on
44              compilation options).
45
46       -E     Ignore environment variables like PYTHONPATH and PYTHONHOME that
47              modify the behavior of the interpreter.
48
49       -h ,  -? ,  --help
50              Prints the usage for the interpreter executable and exits.
51
52       -i     When  a  script  is passed as first argument or the -c option is
53              used, enter interactive mode after executing the script  or  the
54              command.  It does not read the $PYTHONSTARTUP file.  This can be
55              useful to inspect global variables  or  a  stack  trace  when  a
56              script raises an exception.
57
58       -m module-name
59              Searches  sys.path for the named module and runs the correspond‐
60              ing .py file as a script.
61
62       -O     Turn on basic optimizations.  This changes the  filename  exten‐
63              sion  for  compiled  (bytecode)  files from .pyc to .pyo.  Given
64              twice, causes docstrings to be discarded.
65
66       -OO    Discard docstrings in addition to the -O optimizations.
67
68       -R     Turn on "hash randomization", so that the hash() values of  str,
69              bytes  and  datetime  objects are "salted" with an unpredictable
70              pseudo-random value.  Although they remain  constant  within  an
71              individual  Python  process,  they  are  not predictable between
72              repeated invocations of Python.
73
74              This is intended to provide protection against a denial of  ser‐
75              vice  caused  by  carefully-chosen inputs that exploit the worst
76              case performance of a dict construction, O(n^2) complexity.  See
77              http://www.ocert.org/advisories/ocert-2011-003.html for details.
78
79       -Q argument
80              Division  control;  see  PEP  238.   The argument must be one of
81              "old" (the default, int/int  and  long/long  return  an  int  or
82              long), "new" (new division semantics, i.e. int/int and long/long
83              returns a float), "warn" (old division semantics with a  warning
84              for int/int and long/long), or "warnall" (old division semantics
85              with a warning for all use of the division operator).  For a use
86              of "warnall", see the Tools/scripts/fixdiv.py script.
87
88       -s     Don't add user site directory to sys.path.
89
90       -S     Disable  the  import  of  the module site and the site-dependent
91              manipulations of sys.path that it entails.
92
93       -t     Issue a warning when a source file mixes  tabs  and  spaces  for
94              indentation  in a way that makes it depend on the worth of a tab
95              expressed in spaces.  Issue an error when the  option  is  given
96              twice.
97
98       -u     Force  stdin,  stdout  and  stderr to be totally unbuffered.  On
99              systems where it matters, also put stdin, stdout and  stderr  in
100              binary  mode.   Note  that there is internal buffering in xread‐
101              lines(), readlines() and file-object  iterators  ("for  line  in
102              sys.stdin")  which  is  not  influenced by this option.  To work
103              around this, you will want to use "sys.stdin.readline()"  inside
104              a "while 1:" loop.
105
106       -v     Print  a  message each time a module is initialized, showing the
107              place (filename or built-in module) from  which  it  is  loaded.
108              When  given twice, print a message for each file that is checked
109              for when searching for a module.  Also provides  information  on
110              module cleanup at exit.
111
112       -V ,  --version
113              Prints the Python version number of the executable and exits.
114
115       -W argument
116              Warning  control.   Python  sometimes  prints warning message to
117              sys.stderr.  A typical warning message has the  following  form:
118              file:line:  category:  message.   By  default,  each  warning is
119              printed once for each source line where it occurs.  This  option
120              controls  how  often  warnings are printed.  Multiple -W options
121              may be given; when a warning matches more than one  option,  the
122              action  for  the  last matching option is performed.  Invalid -W
123              options are ignored (a warning message is printed about  invalid
124              options when the first warning is issued).  Warnings can also be
125              controlled from within a Python program using the warnings  mod‐
126              ule.
127
128              The  simplest  form  of  argument is one of the following action
129              strings (or a unique abbreviation): ignore to ignore  all  warn‐
130              ings; default to explicitly request the default behavior (print‐
131              ing each warning once per source line); all to print  a  warning
132              each  time it occurs (this may generate many messages if a warn‐
133              ing is triggered repeatedly for the same source  line,  such  as
134              inside a loop); module to print each warning only the first time
135              it occurs in each module; once to print each  warning  only  the
136              first time it occurs in the program; or error to raise an excep‐
137              tion instead of printing a warning message.
138
139              The  full  form  of  argument  is   action:message:category:mod‐
140              ule:line.   Here,  action is as explained above but only applies
141              to messages that match the remaining fields.  Empty fields match
142              all  values;  trailing empty fields may be omitted.  The message
143              field matches the start of the  warning  message  printed;  this
144              match is case-insensitive.  The category field matches the warn‐
145              ing category.  This must be a class name; the match test whether
146              the  actual warning category of the message is a subclass of the
147              specified warning category.  The full class name must be  given.
148              The module field matches the (fully-qualified) module name; this
149              match is case-sensitive.  The line field matches the  line  num‐
150              ber,  where zero matches all line numbers and is thus equivalent
151              to an omitted line number.
152
153       -x     Skip the first line of the source.  This is intended for  a  DOS
154              specific hack only.  Warning: the line numbers in error messages
155              will be off by one!
156
157       -3     Warn about Python 3.x incompatibilities that 2to3  cannot  triv‐
158              ially fix.
159

INTERPRETER INTERFACE

161       The interpreter interface resembles that of the UNIX shell: when called
162       with standard input connected to a tty device, it prompts for  commands
163       and  executes  them  until an EOF is read; when called with a file name
164       argument or with a file as standard input,  it  reads  and  executes  a
165       script  from  that  file;  when called with -c command, it executes the
166       Python statement(s) given as command.  Here command may contain  multi‐
167       ple  statements  separated by newlines.  Leading whitespace is signifi‐
168       cant in Python statements!  In non-interactive mode, the  entire  input
169       is parsed before it is executed.
170
171       If  available,  the script name and additional arguments thereafter are
172       passed to the script in the Python variable sys.argv, which is  a  list
173       of  strings (you must first import sys to be able to access it).  If no
174       script name is given, sys.argv[0] is an empty string; if  -c  is  used,
175       sys.argv[0] contains the string '-c'.  Note that options interpreted by
176       the Python interpreter itself are not placed in sys.argv.
177
178       In interactive mode, the primary prompt is  `>>>';  the  second  prompt
179       (which  appears  when a command is not complete) is `...'.  The prompts
180       can be changed by assignment to sys.ps1 or  sys.ps2.   The  interpreter
181       quits  when  it  reads an EOF at a prompt.  When an unhandled exception
182       occurs, a stack trace is printed and control  returns  to  the  primary
183       prompt;  in  non-interactive mode, the interpreter exits after printing
184       the stack trace.  The interrupt  signal  raises  the  KeyboardInterrupt
185       exception;  other  UNIX  signals are not caught (except that SIGPIPE is
186       sometimes ignored, in favor of the IOError exception).  Error  messages
187       are written to stderr.
188

FILES AND DIRECTORIES

190       These are subject to difference depending on local installation conven‐
191       tions; ${prefix}  and  ${exec_prefix}  are  installation-dependent  and
192       should  be  interpreted as for GNU software; they may be the same.  The
193       default for both is /usr/local.
194
195       ${exec_prefix}/bin/python
196              Recommended location of the interpreter.
197
198       ${prefix}/lib/python<version>
199       ${exec_prefix}/lib/python<version>
200              Recommended locations of the directories containing the standard
201              modules.
202
203       ${prefix}/include/python<version>
204       ${exec_prefix}/include/python<version>
205              Recommended  locations of the directories containing the include
206              files needed for developing Python extensions and embedding  the
207              interpreter.
208
209       ~/.pythonrc.py
210              User-specific initialization file loaded by the user module; not
211              used by default or by most applications.
212

ENVIRONMENT VARIABLES

214       PYTHONHOME
215              Change the  location  of  the  standard  Python  libraries.   By
216              default, the libraries are searched in ${prefix}/lib/python<ver‐
217              sion> and  ${exec_prefix}/lib/python<version>,  where  ${prefix}
218              and  ${exec_prefix} are installation-dependent directories, both
219              defaulting to /usr/local.  When $PYTHONHOME is set to  a  single
220              directory, its value replaces both ${prefix} and ${exec_prefix}.
221              To specify different values for these, set $PYTHONHOME to ${pre‐
222              fix}:${exec_prefix}.
223
224       PYTHONPATH
225              Augments  the  default search path for module files.  The format
226              is the same as the shell's $PATH: one or  more  directory  path‐
227              names   separated   by  colons.   Non-existent  directories  are
228              silently ignored.   The  default  search  path  is  installation
229              dependent,  but  generally begins with ${prefix}/lib/python<ver‐
230              sion> (see PYTHONHOME above).  The default search path is always
231              appended  to  $PYTHONPATH.   If  a script argument is given, the
232              directory containing the script is inserted in the path in front
233              of  $PYTHONPATH.  The search path can be manipulated from within
234              a Python program as the variable sys.path.
235
236       PYTHONSTARTUP
237              If this is the name of a readable file, the Python  commands  in
238              that  file  are executed before the first prompt is displayed in
239              interactive mode.  The file is executed in the same  name  space
240              where  interactive commands are executed so that objects defined
241              or imported in it can  be  used  without  qualification  in  the
242              interactive  session.   You  can also change the prompts sys.ps1
243              and sys.ps2 in this file.
244
245       PYTHONY2K
246              Set this to a non-empty string  to  cause  the  time  module  to
247              require  dates  specified  as  strings to include 4-digit years,
248              otherwise 2-digit years are converted based on  rules  described
249              in the time module documentation.
250
251       PYTHONOPTIMIZE
252              If  this is set to a non-empty string it is equivalent to speci‐
253              fying the -O option. If set to an integer, it is  equivalent  to
254              specifying -O multiple times.
255
256       PYTHONDEBUG
257              If  this is set to a non-empty string it is equivalent to speci‐
258              fying the -d option. If set to an integer, it is  equivalent  to
259              specifying -d multiple times.
260
261       PYTHONDONTWRITEBYTECODE
262              If  this is set to a non-empty string it is equivalent to speci‐
263              fying the -B option (don't try to write .py[co] files).
264
265       PYTHONINSPECT
266              If this is set to a non-empty string it is equivalent to  speci‐
267              fying the -i option.
268
269       PYTHONIOENCODING
270              If  this is set before running the interpreter, it overrides the
271              encoding used for stdin/stdout/stderr, in the  syntax  encoding‐
272              name:errorhandler  The errorhandler part is optional and has the
273              same meaning as in str.encode. For stderr, the errorhandler
274               part is ignored; the handler will always be ´backslashreplace´.
275
276       PYTHONNOUSERSITE
277              If this is set to a non-empty string it is equivalent to  speci‐
278              fying  the  -s  option  (Don't  add  the  user site directory to
279              sys.path).
280
281       PYTHONUNBUFFERED
282              If this is set to a non-empty string it is equivalent to  speci‐
283              fying the -u option.
284
285       PYTHONVERBOSE
286              If  this is set to a non-empty string it is equivalent to speci‐
287              fying the -v option. If set to an integer, it is  equivalent  to
288              specifying -v multiple times.
289
290       PYTHONWARNINGS
291              If  this  is set to a comma-separated string it is equivalent to
292              specifying the -W option for each separate value.
293
294       PYTHONHASHSEED
295              If this variable is set to "random", the effect is the  same  as
296              specifying  the  -R  option:  a random value is used to seed the
297              hashes of str, bytes and datetime objects.
298
299              If PYTHONHASHSEED is set to an integer value, it is  used  as  a
300              fixed seed for generating the hash() of the types covered by the
301              hash randomization.  Its purpose is to allow repeatable hashing,
302              such  as for selftests for the interpreter itself, or to allow a
303              cluster of python processes to share hash values.
304
305              The  integer  must  be   a   decimal   number   in   the   range
306              [0,4294967295].   Specifying  the  value 0 will lead to the same
307              hash values as when hash randomization is disabled.
308

AUTHOR

310       The Python Software Foundation: https://www.python.org/psf/
311

INTERNET RESOURCES

313       Main website:  https://www.python.org/
314       Documentation:  https://docs.python.org/2/
315       Developer resources:  https://docs.python.org/devguide/
316       Downloads:  https://www.python.org/downloads/
317       Module repository:  https://pypi.python.org/
318       Newsgroups:  comp.lang.python, comp.lang.python.announce
319

LICENSING

321       Python is distributed under an  Open  Source  license.   See  the  file
322       "LICENSE"  in the Python source distribution for information on terms &
323       conditions for accessing and otherwise using  Python  and  for  a  DIS‐
324       CLAIMER OF ALL WARRANTIES.
325
326
327
328                                                                     PYTHON(1)
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