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
24 RESOURCES 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(bytear‐
39 ray_instance) and comparing bytes/bytearray with str. (-bb:
40 issue errors)
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.
75 -O Remove assert statements and any code conditional on the value
77 of __debug__; augment the filename for compiled (bytecode) files
78 by adding .opt-1 before the .pyc extension.
79 -OO Do -O and also discard docstrings; change the filename for com‐
81 piled (bytecode) files by adding .opt-2 before the .pyc exten‐
82 sion.
83 -q Do not print the version and copyright messages. These messages
85 are also suppressed in non-interactive mode.
86 -s Don't add user site directory to sys.path.
88 -S Disable the import of the module site and the site-dependent
90 manipulations of sys.path that it entails. Also disable these
91 manipulations if site is explicitly imported later.
92 -u Force the stdout and stderr streams to be unbuffered. This
94 option has no effect on the stdin stream.
95 -v Print a message each time a module is initialized, showing the
97 place (filename or built-in module) from which it is loaded.
98 When given twice, print a message for each file that is checked
99 for when searching for a module. Also provides information on
100 module cleanup at exit.
101 -V , --version
103 Prints the Python version number of the executable and exits.
104 When given twice, print more information about the build.
105 -W argument
107 Warning control. Python sometimes prints warning message to
108 sys.stderr. A typical warning message has the following form:
109 file:line: category: message. By default, each warning is
110 printed once for each source line where it occurs. This option
111 controls how often warnings are printed. Multiple -W options
112 may be given; when a warning matches more than one option, the
113 action for the last matching option is performed. Invalid -W
114 options are ignored (a warning message is printed about invalid
115 options when the first warning is issued). Warnings can also be
116 controlled from within a Python program using the warnings mod‐
117 ule.
118 The simplest form of argument is one of the following action
120 strings (or a unique abbreviation): ignore to ignore all warn‐
121 ings; default to explicitly request the default behavior (print‐
122 ing each warning once per source line); all to print a warning
123 each time it occurs (this may generate many messages if a warn‐
124 ing is triggered repeatedly for the same source line, such as
125 inside a loop); module to print each warning only the first time
126 it occurs in each module; once to print each warning only the
127 first time it occurs in the program; or error to raise an excep‐
128 tion instead of printing a warning message.
129 The full form of argument is action:message:category:mod‐
131 ule:line. Here, action is as explained above but only applies
132 to messages that match the remaining fields. Empty fields match
133 all values; trailing empty fields may be omitted. The message
134 field matches the start of the warning message printed; this
135 match is case-insensitive. The category field matches the warn‐
136 ing category. This must be a class name; the match test whether
137 the actual warning category of the message is a subclass of the
138 specified warning category. The full class name must be given.
139 The module field matches the (fully-qualified) module name; this
140 match is case-sensitive. The line field matches the line num‐
141 ber, where zero matches all line numbers and is thus equivalent
142 to an omitted line number.
143 -X option
145 Set implementation specific option. The following options are
146 available:
147 -X faulthandler: enable faulthandler
149 -X showrefcount: output the total reference count and number
151 of used
152 memory blocks when the program finishes or after each
153 statement in the
154 interactive interpreter. This only works on debug builds
155 -X tracemalloc: start tracing Python memory allocations
157 using the
158 tracemalloc module. By default, only the most recent
159 frame is stored in a
160 traceback of a trace. Use -X tracemalloc=NFRAME to start
161 tracing with a
162 traceback limit of NFRAME frames
163 -X showalloccount: output the total count of allocated
165 objects for each
166 type when the program finishes. This only works when
167 Python was built with
168 COUNT_ALLOCS defined
169 -X importtime: show how long each import takes. It shows
171 module name,
172 cumulative time (including nested imports) and self time
173 (excluding
174 nested imports). Note that its output may be broken in
175 multi-threaded
176 application. Typical usage is python3 -X importtime -c
177 'import asyncio'
178 -X dev: enable CPython's "development mode", introducing
180 additional runtime
181 checks which are too expensive to be enabled by default.
182 It will not be
183 more verbose than the default if the code is correct:
184 new warnings are
185 only emitted when an issue is detected. Effect of the
186 developer mode:
187 * Add default warning filter, as -W default
188 * Install debug hooks on memory allocators: see the
189 PyMem_SetupDebugHooks() C function
190 * Enable the faulthandler module to dump the Python
191 traceback on a crash
192 * Enable asyncio debug mode
193 * Set the dev_mode attribute of sys.flags to True
194 * io.IOBase destructor logs close() exceptions
195 -X utf8: enable UTF-8 mode for operating system interfaces,
197 overriding the default
198 locale-aware mode. -X utf8=0 explicitly disables UTF-8
199 mode (even when it would
200 otherwise activate automatically). See PYTHONUTF8 for
201 more details
202 -X pycache_prefix=PATH: enable writing .pyc files to a par‐
204 allel tree rooted at the
205 given directory instead of to the code tree.
206 -x Skip the first line of the source. This is intended for a DOS
208 specific hack only. Warning: the line numbers in error messages
209 will be off by one!
210
212 The interpreter interface resembles that of the UNIX shell: when called
213 with standard input connected to a tty device, it prompts for commands
214 and executes them until an EOF is read; when called with a file name
215 argument or with a file as standard input, it reads and executes a
216 script from that file; when called with -c command, it executes the
217 Python statement(s) given as command. Here command may contain multi‐
218 ple statements separated by newlines. Leading whitespace is signifi‐
219 cant in Python statements! In non-interactive mode, the entire input
220 is parsed before it is executed.
221 If available, the script name and additional arguments thereafter are
223 passed to the script in the Python variable sys.argv, which is a list
224 of strings (you must first import sys to be able to access it). If no
225 script name is given, sys.argv[0] is an empty string; if -c is used,
226 sys.argv[0] contains the string '-c'. Note that options interpreted by
227 the Python interpreter itself are not placed in sys.argv.
228 In interactive mode, the primary prompt is `>>>'; the second prompt
230 (which appears when a command is not complete) is `...'. The prompts
231 can be changed by assignment to sys.ps1 or sys.ps2. The interpreter
232 quits when it reads an EOF at a prompt. When an unhandled exception
233 occurs, a stack trace is printed and control returns to the primary
234 prompt; in non-interactive mode, the interpreter exits after printing
235 the stack trace. The interrupt signal raises the KeyboardInterrupt
236 exception; other UNIX signals are not caught (except that SIGPIPE is
237 sometimes ignored, in favor of the IOError exception). Error messages
238 are written to stderr.
239
241 These are subject to difference depending on local installation conven‐
242 tions; ${prefix} and ${exec_prefix} are installation-dependent and
243 should be interpreted as for GNU software; they may be the same. The
244 default for both is /usr/local.
245 ${exec_prefix}/bin/python
247 Recommended location of the interpreter.
248 ${prefix}/lib/python<version>
250 ${exec_prefix}/lib/python<version>
251 Recommended locations of the directories containing the standard
252 modules.
253 ${prefix}/include/python<version>
255 ${exec_prefix}/include/python<version>
256 Recommended locations of the directories containing the include
257 files needed for developing Python extensions and embedding the
258 interpreter.
259
261 PYTHONHOME
262 Change the location of the standard Python libraries. By
263 default, the libraries are searched in ${prefix}/lib/python<ver‐
264 sion> and ${exec_prefix}/lib/python<version>, where ${prefix}
265 and ${exec_prefix} are installation-dependent directories, both
266 defaulting to /usr/local. When $PYTHONHOME is set to a single
267 directory, its value replaces both ${prefix} and ${exec_prefix}.
268 To specify different values for these, set $PYTHONHOME to ${pre‐
269 fix}:${exec_prefix}.
270 PYTHONPATH
272 Augments the default search path for module files. The format
273 is the same as the shell's $PATH: one or more directory path‐
274 names separated by colons. Non-existent directories are
275 silently ignored. The default search path is installation
276 dependent, but generally begins with ${prefix}/lib/python<ver‐
277 sion> (see PYTHONHOME above). The default search path is always
278 appended to $PYTHONPATH. If a script argument is given, the
279 directory containing the script is inserted in the path in front
280 of $PYTHONPATH. The search path can be manipulated from within
281 a Python program as the variable sys.path.
282 PYTHONSTARTUP
284 If this is the name of a readable file, the Python commands in
285 that file are executed before the first prompt is displayed in
286 interactive mode. The file is executed in the same name space
287 where interactive commands are executed so that objects defined
288 or imported in it can be used without qualification in the
289 interactive session. You can also change the prompts sys.ps1
290 and sys.ps2 in this file.
291 PYTHONOPTIMIZE
293 If this is set to a non-empty string it is equivalent to speci‐
294 fying the -O option. If set to an integer, it is equivalent to
295 specifying -O multiple times.
296 PYTHONDEBUG
298 If this is set to a non-empty string it is equivalent to speci‐
299 fying the -d option. If set to an integer, it is equivalent to
300 specifying -d multiple times.
301 PYTHONDONTWRITEBYTECODE
303 If this is set to a non-empty string it is equivalent to speci‐
304 fying the -B option (don't try to write .pyc files).
305 PYTHONINSPECT
307 If this is set to a non-empty string it is equivalent to speci‐
308 fying the -i option.
309 PYTHONIOENCODING
311 If this is set before running the interpreter, it overrides the
312 encoding used for stdin/stdout/stderr, in the syntax encoding‐
313 name:errorhandler The errorhandler part is optional and has the
314 same meaning as in str.encode. For stderr, the errorhandler
315 part is ignored; the handler will always be ´backslashreplace´.
316 PYTHONNOUSERSITE
318 If this is set to a non-empty string it is equivalent to speci‐
319 fying the -s option (Don't add the user site directory to
320 sys.path).
321 PYTHONUNBUFFERED
323 If this is set to a non-empty string it is equivalent to speci‐
324 fying the -u option.
325 PYTHONVERBOSE
327 If this is set to a non-empty string it is equivalent to speci‐
328 fying the -v option. If set to an integer, it is equivalent to
329 specifying -v multiple times.
330 PYTHONWARNINGS
332 If this is set to a comma-separated string it is equivalent to
333 specifying the -W option for each separate value.
334 PYTHONHASHSEED
336 If this variable is set to "random", a random value is used to
337 seed the hashes of str and bytes objects.
338 If PYTHONHASHSEED is set to an integer value, it is used as a
340 fixed seed for generating the hash() of the types covered by the
341 hash randomization. Its purpose is to allow repeatable hashing,
342 such as for selftests for the interpreter itself, or to allow a
343 cluster of python processes to share hash values.
344 The integer must be a decimal number in the range
346 [0,4294967295]. Specifying the value 0 will disable hash ran‐
347 domization.
348 PYTHONMALLOC
350 Set the Python memory allocators and/or install debug hooks. The
351 available memory allocators are malloc and pymalloc. The avail‐
352 able debug hooks are debug, malloc_debug, and pymalloc_debug.
353 When Python is compiled in debug mode, the default is pymal‐
355 loc_debug and the debug hooks are automatically used. Otherwise,
356 the default is pymalloc.
357 PYTHONMALLOCSTATS
359 If set to a non-empty string, Python will print statistics of
360 the pymalloc memory allocator every time a new pymalloc object
361 arena is created, and on shutdown.
362 This variable is ignored if the $PYTHONMALLOC environment vari‐
364 able is used to force the malloc(3) allocator of the C library,
365 or if Python is configured without pymalloc support.
366 PYTHONASYNCIODEBUG
368 If this environment variable is set to a non-empty string,
369 enable the debug mode of the asyncio module.
370 PYTHONTRACEMALLOC
372 If this environment variable is set to a non-empty string, start
373 tracing Python memory allocations using the tracemalloc module.
374 The value of the variable is the maximum number of frames stored
376 in a traceback of a trace. For example, PYTHONTRACEMALLOC=1
377 stores only the most recent frame.
378 PYTHONFAULTHANDLER
380 If this environment variable is set to a non-empty string,
381 faulthandler.enable() is called at startup: install a handler
382 for SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL signals to dump
383 the Python traceback.
384 This is equivalent to the -X faulthandler option.
386 PYTHONEXECUTABLE
388 If this environment variable is set, sys.argv[0] will be set to
389 its value instead of the value got through the C runtime. Only
390 works on Mac OS X.
391 PYTHONUSERBASE
393 Defines the user base directory, which is used to compute the
394 path of the user site-packages directory and Distutils installa‐
395 tion paths for python setup.py install --user.
396 PYTHONPROFILEIMPORTTIME
398 If this environment variable is set to a non-empty string,
399 Python will show how long each import takes. This is exactly
400 equivalent to setting -X importtime on the command line.
401 PYTHONBREAKPOINT
403 If this environment variable is set to 0, it disables the
404 default debugger. It can be set to the callable of your debugger
405 of choice.
406 Debug-mode variables
408 Setting these variables only has an effect in a debug build of Python,
409 that is, if Python was configured with the --with-pydebug build option.
410 PYTHONTHREADDEBUG
412 If this environment variable is set, Python will print threading
413 debug info.
414 PYTHONDUMPREFS
416 If this environment variable is set, Python will dump objects
417 and reference counts still alive after shutting down the inter‐
418 preter.
419
421 The Python Software Foundation: https://www.python.org/psf/
422
424 Main website: https://www.python.org/
425 Documentation: https://docs.python.org/
426 Developer resources: https://devguide.python.org/
427 Downloads: https://www.python.org/downloads/
428 Module repository: https://pypi.org/
429 Newsgroups: comp.lang.python, comp.lang.python.announce
430
432 Python is distributed under an Open Source license. See the file
433 "LICENSE" in the Python source distribution for information on terms &
434 conditions for accessing and otherwise using Python and for a DIS‐
435 CLAIMER OF ALL WARRANTIES.
436 PYTHON(1)