1PYTHON(1) General Commands Manual PYTHON(1)
2
6 python - an interpreted, interactive, object-oriented programming lan‐
7 guage
8
10 python [ -B ] [ -b ] [ -d ] [ -E ] [ -h ] [ -i ] [ -I ]
11 [ -m module-name ] [ -q ] [ -O ] [ -OO ] [ -s ] [ -S ] [ -u ]
12 [ -v ] [ -V ] [ -W argument ] [ -x ] [ -X option ] [ -? ]
13 [ --check-hash-based-pycs default | always | never ]
14 [ -c command | script | - ] [ arguments ]
15
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 RE‐
24 SOURCES below; they may be installed on your system as well.)
25 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 Documentation for installed Python modules and packages can be viewed
32 by running the pydoc program.
33
35 -B Don't write .pyc files on import. See also PYTHONDONTWRITEBYTE‐
36 CODE.
37 -b Issue warnings about str(bytes_instance), str(bytearray_in‐
39 stance) and comparing bytes/bytearray with str. (-bb: issue er‐
40 rors)
41 -c command
43 Specify the command to execute (see next section). This termi‐
44 nates the option list (following options are passed as arguments
45 to the command).
46 --check-hash-based-pycs mode
48 Configure how Python evaluates the up-to-dateness of hash-based
49 .pyc files.
50 -d Turn on parser debugging output (for expert only, depending on
52 compilation options).
53 -E Ignore environment variables like PYTHONPATH and PYTHONHOME that
55 modify the behavior of the interpreter.
56 -h , -? , --help
58 Prints the usage for the interpreter executable and exits.
59 -i When a script is passed as first argument or the -c option is
61 used, enter interactive mode after executing the script or the
62 command. It does not read the $PYTHONSTARTUP file. This can be
63 useful to inspect global variables or a stack trace when a
64 script raises an exception.
65 -I Run Python in isolated mode. This also implies -E and -s. In
67 isolated mode sys.path contains neither the script's directory
68 nor the user's site-packages directory. All PYTHON* environment
69 variables are ignored, too. Further restrictions may be imposed
70 to prevent the user from injecting malicious code.
71 -m module-name
73 Searches sys.path for the named module and runs the correspond‐
74 ing .py file as a script. This terminates the option list (fol‐
75 lowing options are passed as arguments to the module).
76 -O Remove assert statements and any code conditional on the value
78 of __debug__; augment the filename for compiled (bytecode) files
79 by adding .opt-1 before the .pyc extension.
80 -OO Do -O and also discard docstrings; change the filename for com‐
82 piled (bytecode) files by adding .opt-2 before the .pyc exten‐
83 sion.
84 -q Do not print the version and copyright messages. These messages
86 are also suppressed in non-interactive mode.
87 -s Don't add user site directory to sys.path.
89 -S Disable the import of the module site and the site-dependent ma‐
91 nipulations of sys.path that it entails. Also disable these ma‐
92 nipulations if site is explicitly imported later.
93 -u Force the stdout and stderr streams to be unbuffered. This op‐
95 tion has no effect on the stdin stream.
96 -v Print a message each time a module is initialized, showing the
98 place (filename or built-in module) from which it is loaded.
99 When given twice, print a message for each file that is checked
100 for when searching for a module. Also provides information on
101 module cleanup at exit.
102 -V , --version
104 Prints the Python version number of the executable and exits.
105 When given twice, print more information about the build.
106 -W argument
109 Warning control. Python's warning machinery by default prints
110 warning messages to sys.stderr.
111 The simplest settings apply a particular action unconditionally
113 to all warnings emitted by a process (even those that are other‐
114 wise ignored by default):
115 -Wdefault # Warn once per call location
117 -Werror # Convert to exceptions
118 -Walways # Warn every time
119 -Wmodule # Warn once per calling module
120 -Wonce # Warn once per Python process
121 -Wignore # Never warn
122 The action names can be abbreviated as desired and the inter‐
124 preter will resolve them to the appropriate action name. For ex‐
125 ample, -Wi is the same as -Wignore .
126 The full form of argument is: action:message:category:mod‐
128 ule:lineno
129 Empty fields match all values; trailing empty fields may be
131 omitted. For example -W ignore::DeprecationWarning ignores all
132 DeprecationWarning warnings.
133 The action field is as explained above but only applies to warn‐
135 ings that match the remaining fields.
136 The message field must match the whole printed warning message;
138 this match is case-insensitive.
139 The category field matches the warning category (ex: "Depreca‐
141 tionWarning"). This must be a class name; the match test whether
142 the actual warning category of the message is a subclass of the
143 specified warning category.
144 The module field matches the (fully-qualified) module name; this
146 match is case-sensitive.
147 The lineno field matches the line number, where zero matches all
149 line numbers and is thus equivalent to an omitted line number.
150 Multiple -W options can be given; when a warning matches more
152 than one option, the action for the last matching option is per‐
153 formed. Invalid -W options are ignored (though, a warning mes‐
154 sage is printed about invalid options when the first warning is
155 issued).
156 Warnings can also be controlled using the PYTHONWARNINGS envi‐
158 ronment variable and from within a Python program using the
159 warnings module. For example, the warnings.filterwarnings()
160 function can be used to use a regular expression on the warning
161 message.
162 -X option
165 Set implementation specific option. The following options are
166 available:
167 -X faulthandler: enable faulthandler
169 -X showrefcount: output the total reference count and number
171 of used
172 memory blocks when the program finishes or after each
173 statement in the
174 interactive interpreter. This only works on debug builds
175 -X tracemalloc: start tracing Python memory allocations us‐
177 ing the
178 tracemalloc module. By default, only the most recent
179 frame is stored in a
180 traceback of a trace. Use -X tracemalloc=NFRAME to start
181 tracing with a
182 traceback limit of NFRAME frames
183 -X importtime: show how long each import takes. It shows
185 module name,
186 cumulative time (including nested imports) and self time
187 (excluding
188 nested imports). Note that its output may be broken in
189 multi-threaded
190 application. Typical usage is python3 -X importtime -c
191 'import asyncio'
192 -X dev: enable CPython's "development mode", introducing ad‐
194 ditional runtime
195 checks which are too expensive to be enabled by default.
196 It will not be
197 more verbose than the default if the code is correct:
198 new warnings are
199 only emitted when an issue is detected. Effect of the
200 developer mode:
201 * Add default warning filter, as -W default
202 * Install debug hooks on memory allocators: see the
203 PyMem_SetupDebugHooks()
204 C function
205 * Enable the faulthandler module to dump the Python
206 traceback on a crash
207 * Enable asyncio debug mode
208 * Set the dev_mode attribute of sys.flags to True
209 * io.IOBase destructor logs close() exceptions
210 -X utf8: enable UTF-8 mode for operating system interfaces,
212 overriding the default
213 locale-aware mode. -X utf8=0 explicitly disables UTF-8
214 mode (even when it would
215 otherwise activate automatically). See PYTHONUTF8 for
216 more details
217 -X pycache_prefix=PATH: enable writing .pyc files to a par‐
219 allel tree rooted at the
220 given directory instead of to the code tree.
221 -X warn_default_encoding: enable opt-in EncodingWarning for
223 'encoding=None'
224 -X int_max_str_digits=number: limit the size of int<->str
226 conversions.
227 This helps avoid denial of service attacks when parsing
228 untrusted data.
229 The default is sys.int_info.default_max_str_digits. 0
230 disables.
231 -x Skip the first line of the source. This is intended for a DOS
234 specific hack only. Warning: the line numbers in error messages
235 will be off by one!
236
238 The interpreter interface resembles that of the UNIX shell: when called
239 with standard input connected to a tty device, it prompts for commands
240 and executes them until an EOF is read; when called with a file name
241 argument or with a file as standard input, it reads and executes a
242 script from that file; when called with -c command, it executes the
243 Python statement(s) given as command. Here command may contain multi‐
244 ple statements separated by newlines. Leading whitespace is signifi‐
245 cant in Python statements! In non-interactive mode, the entire input
246 is parsed before it is executed.
247 If available, the script name and additional arguments thereafter are
249 passed to the script in the Python variable sys.argv, which is a list
250 of strings (you must first import sys to be able to access it). If no
251 script name is given, sys.argv[0] is an empty string; if -c is used,
252 sys.argv[0] contains the string '-c'. Note that options interpreted by
253 the Python interpreter itself are not placed in sys.argv.
254 In interactive mode, the primary prompt is `>>>'; the second prompt
256 (which appears when a command is not complete) is `...'. The prompts
257 can be changed by assignment to sys.ps1 or sys.ps2. The interpreter
258 quits when it reads an EOF at a prompt. When an unhandled exception
259 occurs, a stack trace is printed and control returns to the primary
260 prompt; in non-interactive mode, the interpreter exits after printing
261 the stack trace. The interrupt signal raises the KeyboardInterrupt ex‐
262 ception; other UNIX signals are not caught (except that SIGPIPE is
263 sometimes ignored, in favor of the IOError exception). Error messages
264 are written to stderr.
265
267 These are subject to difference depending on local installation conven‐
268 tions; ${prefix} and ${exec_prefix} are installation-dependent and
269 should be interpreted as for GNU software; they may be the same. The
270 default for both is /usr/local.
271 ${exec_prefix}/bin/python
273 Recommended location of the interpreter.
274 ${prefix}/lib/python<version>
276 ${exec_prefix}/lib/python<version>
277 Recommended locations of the directories containing the standard
278 modules.
279 ${prefix}/include/python<version>
281 ${exec_prefix}/include/python<version>
282 Recommended locations of the directories containing the include
283 files needed for developing Python extensions and embedding the
284 interpreter.
285
287 PYTHONHOME
288 Change the location of the standard Python libraries. By de‐
289 fault, the libraries are searched in ${prefix}/lib/python<ver‐
290 sion> and ${exec_prefix}/lib/python<version>, where ${prefix}
291 and ${exec_prefix} are installation-dependent directories, both
292 defaulting to /usr/local. When $PYTHONHOME is set to a single
293 directory, its value replaces both ${prefix} and ${exec_prefix}.
294 To specify different values for these, set $PYTHONHOME to ${pre‐
295 fix}:${exec_prefix}.
296 PYTHONPATH
298 Augments the default search path for module files. The format
299 is the same as the shell's $PATH: one or more directory path‐
300 names separated by colons. Non-existent directories are
301 silently ignored. The default search path is installation de‐
302 pendent, but generally begins with ${prefix}/lib/python<version>
303 (see PYTHONHOME above). The default search path is always ap‐
304 pended to $PYTHONPATH. If a script argument is given, the di‐
305 rectory containing the script is inserted in the path in front
306 of $PYTHONPATH. The search path can be manipulated from within
307 a Python program as the variable sys.path.
308 PYTHONPLATLIBDIR
310 Override sys.platlibdir.
311 PYTHONSTARTUP
313 If this is the name of a readable file, the Python commands in
314 that file are executed before the first prompt is displayed in
315 interactive mode. The file is executed in the same name space
316 where interactive commands are executed so that objects defined
317 or imported in it can be used without qualification in the in‐
318 teractive session. You can also change the prompts sys.ps1 and
319 sys.ps2 in this file.
320 PYTHONOPTIMIZE
322 If this is set to a non-empty string it is equivalent to speci‐
323 fying the -O option. If set to an integer, it is equivalent to
324 specifying -O multiple times.
325 PYTHONDEBUG
327 If this is set to a non-empty string it is equivalent to speci‐
328 fying the -d option. If set to an integer, it is equivalent to
329 specifying -d multiple times.
330 PYTHONDONTWRITEBYTECODE
332 If this is set to a non-empty string it is equivalent to speci‐
333 fying the -B option (don't try to write .pyc files).
334 PYTHONINSPECT
336 If this is set to a non-empty string it is equivalent to speci‐
337 fying the -i option.
338 PYTHONIOENCODING
340 If this is set before running the interpreter, it overrides the
341 encoding used for stdin/stdout/stderr, in the syntax encoding‐
342 name:errorhandler The errorhandler part is optional and has the
343 same meaning as in str.encode. For stderr, the errorhandler
344 part is ignored; the handler will always be ´backslashreplace´.
345 PYTHONNOUSERSITE
347 If this is set to a non-empty string it is equivalent to speci‐
348 fying the -s option (Don't add the user site directory to
349 sys.path).
350 PYTHONUNBUFFERED
352 If this is set to a non-empty string it is equivalent to speci‐
353 fying the -u option.
354 PYTHONVERBOSE
356 If this is set to a non-empty string it is equivalent to speci‐
357 fying the -v option. If set to an integer, it is equivalent to
358 specifying -v multiple times.
359 PYTHONWARNINGS
361 If this is set to a comma-separated string it is equivalent to
362 specifying the -W option for each separate value.
363 PYTHONHASHSEED
365 If this variable is set to "random", a random value is used to
366 seed the hashes of str and bytes objects.
367 If PYTHONHASHSEED is set to an integer value, it is used as a
369 fixed seed for generating the hash() of the types covered by the
370 hash randomization. Its purpose is to allow repeatable hashing,
371 such as for selftests for the interpreter itself, or to allow a
372 cluster of python processes to share hash values.
373 The integer must be a decimal number in the range
375 [0,4294967295]. Specifying the value 0 will disable hash ran‐
376 domization.
377 PYTHONINTMAXSTRDIGITS
379 Limit the maximum digit characters in an int value when convert‐
380 ing from a string and when converting an int back to a str. A
381 value of 0 disables the limit. Conversions to or from bases 2,
382 4, 8, 16, and 32 are never limited.
383 PYTHONMALLOC
385 Set the Python memory allocators and/or install debug hooks. The
386 available memory allocators are malloc and pymalloc. The avail‐
387 able debug hooks are debug, malloc_debug, and pymalloc_debug.
388 When Python is compiled in debug mode, the default is pymal‐
390 loc_debug and the debug hooks are automatically used. Otherwise,
391 the default is pymalloc.
392 PYTHONMALLOCSTATS
394 If set to a non-empty string, Python will print statistics of
395 the pymalloc memory allocator every time a new pymalloc object
396 arena is created, and on shutdown.
397 This variable is ignored if the $PYTHONMALLOC environment vari‐
399 able is used to force the malloc(3) allocator of the C library,
400 or if Python is configured without pymalloc support.
401 PYTHONASYNCIODEBUG
403 If this environment variable is set to a non-empty string, en‐
404 able the debug mode of the asyncio module.
405 PYTHONTRACEMALLOC
407 If this environment variable is set to a non-empty string, start
408 tracing Python memory allocations using the tracemalloc module.
409 The value of the variable is the maximum number of frames stored
411 in a traceback of a trace. For example, PYTHONTRACEMALLOC=1
412 stores only the most recent frame.
413 PYTHONFAULTHANDLER
415 If this environment variable is set to a non-empty string,
416 faulthandler.enable() is called at startup: install a handler
417 for SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL signals to dump
418 the Python traceback.
419 This is equivalent to the -X faulthandler option.
421 PYTHONEXECUTABLE
423 If this environment variable is set, sys.argv[0] will be set to
424 its value instead of the value got through the C runtime. Only
425 works on Mac OS X.
426 PYTHONUSERBASE
428 Defines the user base directory, which is used to compute the
429 path of the user site-packages directory and Distutils installa‐
430 tion paths for python setup.py install --user.
431 PYTHONPROFILEIMPORTTIME
433 If this environment variable is set to a non-empty string,
434 Python will show how long each import takes. This is exactly
435 equivalent to setting -X importtime on the command line.
436 PYTHONBREAKPOINT
438 If this environment variable is set to 0, it disables the de‐
439 fault debugger. It can be set to the callable of your debugger
440 of choice.
441 Debug-mode variables
443 Setting these variables only has an effect in a debug build of Python,
444 that is, if Python was configured with the --with-pydebug build option.
445 PYTHONTHREADDEBUG
447 If this environment variable is set, Python will print threading
448 debug info. The feature is deprecated in Python 3.10 and will
449 be removed in Python 3.12.
450 PYTHONDUMPREFS
452 If this environment variable is set, Python will dump objects
453 and reference counts still alive after shutting down the inter‐
454 preter.
455
457 The Python Software Foundation: https://www.python.org/psf/
458
460 Main website: https://www.python.org/
461 Documentation: https://docs.python.org/
462 Developer resources: https://devguide.python.org/
463 Downloads: https://www.python.org/downloads/
464 Module repository: https://pypi.org/
465 Newsgroups: comp.lang.python, comp.lang.python.announce
466
468 Python is distributed under an Open Source license. See the file "LI‐
469 CENSE" in the Python source distribution for information on terms &
470 conditions for accessing and otherwise using Python and for a DIS‐
471 CLAIMER OF ALL WARRANTIES.
472 PYTHON(1)