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 importtime: show how long each import takes. It shows
165 module name,
166 cumulative time (including nested imports) and self time
167 (excluding
168 nested imports). Note that its output may be broken in
169 multi-threaded
170 application. Typical usage is python3 -X importtime -c
171 'import asyncio'
172 -X dev: enable CPython's "development mode", introducing
174 additional runtime
175 checks which are too expensive to be enabled by default.
176 It will not be
177 more verbose than the default if the code is correct:
178 new warnings are
179 only emitted when an issue is detected. Effect of the
180 developer mode:
181 * Add default warning filter, as -W default
182 * Install debug hooks on memory allocators: see the
183 PyMem_SetupDebugHooks() C function
184 * Enable the faulthandler module to dump the Python
185 traceback on a crash
186 * Enable asyncio debug mode
187 * Set the dev_mode attribute of sys.flags to True
188 * io.IOBase destructor logs close() exceptions
189 -X utf8: enable UTF-8 mode for operating system interfaces,
191 overriding the default
192 locale-aware mode. -X utf8=0 explicitly disables UTF-8
193 mode (even when it would
194 otherwise activate automatically). See PYTHONUTF8 for
195 more details
196 -X pycache_prefix=PATH: enable writing .pyc files to a par‐
198 allel tree rooted at the
199 given directory instead of to the code tree.
200 -x Skip the first line of the source. This is intended for a DOS
202 specific hack only. Warning: the line numbers in error messages
203 will be off by one!
204
206 The interpreter interface resembles that of the UNIX shell: when called
207 with standard input connected to a tty device, it prompts for commands
208 and executes them until an EOF is read; when called with a file name
209 argument or with a file as standard input, it reads and executes a
210 script from that file; when called with -c command, it executes the
211 Python statement(s) given as command. Here command may contain multi‐
212 ple statements separated by newlines. Leading whitespace is signifi‐
213 cant in Python statements! In non-interactive mode, the entire input
214 is parsed before it is executed.
215 If available, the script name and additional arguments thereafter are
217 passed to the script in the Python variable sys.argv, which is a list
218 of strings (you must first import sys to be able to access it). If no
219 script name is given, sys.argv[0] is an empty string; if -c is used,
220 sys.argv[0] contains the string '-c'. Note that options interpreted by
221 the Python interpreter itself are not placed in sys.argv.
222 In interactive mode, the primary prompt is `>>>'; the second prompt
224 (which appears when a command is not complete) is `...'. The prompts
225 can be changed by assignment to sys.ps1 or sys.ps2. The interpreter
226 quits when it reads an EOF at a prompt. When an unhandled exception
227 occurs, a stack trace is printed and control returns to the primary
228 prompt; in non-interactive mode, the interpreter exits after printing
229 the stack trace. The interrupt signal raises the KeyboardInterrupt
230 exception; other UNIX signals are not caught (except that SIGPIPE is
231 sometimes ignored, in favor of the IOError exception). Error messages
232 are written to stderr.
233
235 These are subject to difference depending on local installation conven‐
236 tions; ${prefix} and ${exec_prefix} are installation-dependent and
237 should be interpreted as for GNU software; they may be the same. The
238 default for both is /usr/local.
239 ${exec_prefix}/bin/python
241 Recommended location of the interpreter.
242 ${prefix}/lib/python<version>
244 ${exec_prefix}/lib/python<version>
245 Recommended locations of the directories containing the standard
246 modules.
247 ${prefix}/include/python<version>
249 ${exec_prefix}/include/python<version>
250 Recommended locations of the directories containing the include
251 files needed for developing Python extensions and embedding the
252 interpreter.
253
255 PYTHONHOME
256 Change the location of the standard Python libraries. By
257 default, the libraries are searched in ${prefix}/lib/python<ver‐
258 sion> and ${exec_prefix}/lib/python<version>, where ${prefix}
259 and ${exec_prefix} are installation-dependent directories, both
260 defaulting to /usr/local. When $PYTHONHOME is set to a single
261 directory, its value replaces both ${prefix} and ${exec_prefix}.
262 To specify different values for these, set $PYTHONHOME to ${pre‐
263 fix}:${exec_prefix}.
264 PYTHONPATH
266 Augments the default search path for module files. The format
267 is the same as the shell's $PATH: one or more directory path‐
268 names separated by colons. Non-existent directories are
269 silently ignored. The default search path is installation
270 dependent, but generally begins with ${prefix}/lib/python<ver‐
271 sion> (see PYTHONHOME above). The default search path is always
272 appended to $PYTHONPATH. If a script argument is given, the
273 directory containing the script is inserted in the path in front
274 of $PYTHONPATH. The search path can be manipulated from within
275 a Python program as the variable sys.path.
276 PYTHONPLATLIBDIR
278 Override sys.platlibdir.
279 PYTHONSTARTUP
281 If this is the name of a readable file, the Python commands in
282 that file are executed before the first prompt is displayed in
283 interactive mode. The file is executed in the same name space
284 where interactive commands are executed so that objects defined
285 or imported in it can be used without qualification in the
286 interactive session. You can also change the prompts sys.ps1
287 and sys.ps2 in this file.
288 PYTHONOPTIMIZE
290 If this is set to a non-empty string it is equivalent to speci‐
291 fying the -O option. If set to an integer, it is equivalent to
292 specifying -O multiple times.
293 PYTHONDEBUG
295 If this is set to a non-empty string it is equivalent to speci‐
296 fying the -d option. If set to an integer, it is equivalent to
297 specifying -d multiple times.
298 PYTHONDONTWRITEBYTECODE
300 If this is set to a non-empty string it is equivalent to speci‐
301 fying the -B option (don't try to write .pyc files).
302 PYTHONINSPECT
304 If this is set to a non-empty string it is equivalent to speci‐
305 fying the -i option.
306 PYTHONIOENCODING
308 If this is set before running the interpreter, it overrides the
309 encoding used for stdin/stdout/stderr, in the syntax encoding‐
310 name:errorhandler The errorhandler part is optional and has the
311 same meaning as in str.encode. For stderr, the errorhandler
312 part is ignored; the handler will always be ´backslashreplace´.
313 PYTHONNOUSERSITE
315 If this is set to a non-empty string it is equivalent to speci‐
316 fying the -s option (Don't add the user site directory to
317 sys.path).
318 PYTHONUNBUFFERED
320 If this is set to a non-empty string it is equivalent to speci‐
321 fying the -u option.
322 PYTHONVERBOSE
324 If this is set to a non-empty string it is equivalent to speci‐
325 fying the -v option. If set to an integer, it is equivalent to
326 specifying -v multiple times.
327 PYTHONWARNINGS
329 If this is set to a comma-separated string it is equivalent to
330 specifying the -W option for each separate value.
331 PYTHONHASHSEED
333 If this variable is set to "random", a random value is used to
334 seed the hashes of str and bytes objects.
335 If PYTHONHASHSEED is set to an integer value, it is used as a
337 fixed seed for generating the hash() of the types covered by the
338 hash randomization. Its purpose is to allow repeatable hashing,
339 such as for selftests for the interpreter itself, or to allow a
340 cluster of python processes to share hash values.
341 The integer must be a decimal number in the range
343 [0,4294967295]. Specifying the value 0 will disable hash ran‐
344 domization.
345 PYTHONMALLOC
347 Set the Python memory allocators and/or install debug hooks. The
348 available memory allocators are malloc and pymalloc. The avail‐
349 able debug hooks are debug, malloc_debug, and pymalloc_debug.
350 When Python is compiled in debug mode, the default is pymal‐
352 loc_debug and the debug hooks are automatically used. Otherwise,
353 the default is pymalloc.
354 PYTHONMALLOCSTATS
356 If set to a non-empty string, Python will print statistics of
357 the pymalloc memory allocator every time a new pymalloc object
358 arena is created, and on shutdown.
359 This variable is ignored if the $PYTHONMALLOC environment vari‐
361 able is used to force the malloc(3) allocator of the C library,
362 or if Python is configured without pymalloc support.
363 PYTHONASYNCIODEBUG
365 If this environment variable is set to a non-empty string,
366 enable the debug mode of the asyncio module.
367 PYTHONTRACEMALLOC
369 If this environment variable is set to a non-empty string, start
370 tracing Python memory allocations using the tracemalloc module.
371 The value of the variable is the maximum number of frames stored
373 in a traceback of a trace. For example, PYTHONTRACEMALLOC=1
374 stores only the most recent frame.
375 PYTHONFAULTHANDLER
377 If this environment variable is set to a non-empty string,
378 faulthandler.enable() is called at startup: install a handler
379 for SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL signals to dump
380 the Python traceback.
381 This is equivalent to the -X faulthandler option.
383 PYTHONEXECUTABLE
385 If this environment variable is set, sys.argv[0] will be set to
386 its value instead of the value got through the C runtime. Only
387 works on Mac OS X.
388 PYTHONUSERBASE
390 Defines the user base directory, which is used to compute the
391 path of the user site-packages directory and Distutils installa‐
392 tion paths for python setup.py install --user.
393 PYTHONPROFILEIMPORTTIME
395 If this environment variable is set to a non-empty string,
396 Python will show how long each import takes. This is exactly
397 equivalent to setting -X importtime on the command line.
398 PYTHONBREAKPOINT
400 If this environment variable is set to 0, it disables the
401 default debugger. It can be set to the callable of your debugger
402 of choice.
403 Debug-mode variables
405 Setting these variables only has an effect in a debug build of Python,
406 that is, if Python was configured with the --with-pydebug build option.
407 PYTHONTHREADDEBUG
409 If this environment variable is set, Python will print threading
410 debug info.
411 PYTHONDUMPREFS
413 If this environment variable is set, Python will dump objects
414 and reference counts still alive after shutting down the inter‐
415 preter.
416
418 The Python Software Foundation: https://www.python.org/psf/
419
421 Main website: https://www.python.org/
422 Documentation: https://docs.python.org/
423 Developer resources: https://devguide.python.org/
424 Downloads: https://www.python.org/downloads/
425 Module repository: https://pypi.org/
426 Newsgroups: comp.lang.python, comp.lang.python.announce
427
429 Python is distributed under an Open Source license. See the file
430 "LICENSE" in the Python source distribution for information on terms &
431 conditions for accessing and otherwise using Python and for a DIS‐
432 CLAIMER OF ALL WARRANTIES.
433 PYTHON(1)