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 -X utf8: enable UTF-8 mode for operating system interfaces,
196 overriding the default
197 locale-aware mode. -X utf8=0 explicitly disables UTF-8
198 mode (even when it would
199 otherwise activate automatically). See PYTHONUTF8 for
200 more details
201 -x Skip the first line of the source. This is intended for a DOS
204 specific hack only. Warning: the line numbers in error messages
205 will be off by one!
206
208 The interpreter interface resembles that of the UNIX shell: when called
209 with standard input connected to a tty device, it prompts for commands
210 and executes them until an EOF is read; when called with a file name
211 argument or with a file as standard input, it reads and executes a
212 script from that file; when called with -c command, it executes the
213 Python statement(s) given as command. Here command may contain multi‐
214 ple statements separated by newlines. Leading whitespace is signifi‐
215 cant in Python statements! In non-interactive mode, the entire input
216 is parsed before it is executed.
217 If available, the script name and additional arguments thereafter are
219 passed to the script in the Python variable sys.argv, which is a list
220 of strings (you must first import sys to be able to access it). If no
221 script name is given, sys.argv[0] is an empty string; if -c is used,
222 sys.argv[0] contains the string '-c'. Note that options interpreted by
223 the Python interpreter itself are not placed in sys.argv.
224 In interactive mode, the primary prompt is `>>>'; the second prompt
226 (which appears when a command is not complete) is `...'. The prompts
227 can be changed by assignment to sys.ps1 or sys.ps2. The interpreter
228 quits when it reads an EOF at a prompt. When an unhandled exception
229 occurs, a stack trace is printed and control returns to the primary
230 prompt; in non-interactive mode, the interpreter exits after printing
231 the stack trace. The interrupt signal raises the KeyboardInterrupt
232 exception; other UNIX signals are not caught (except that SIGPIPE is
233 sometimes ignored, in favor of the IOError exception). Error messages
234 are written to stderr.
235
237 These are subject to difference depending on local installation conven‐
238 tions; ${prefix} and ${exec_prefix} are installation-dependent and
239 should be interpreted as for GNU software; they may be the same. The
240 default for both is /usr/local.
241 ${exec_prefix}/bin/python
243 Recommended location of the interpreter.
244 ${prefix}/lib/python<version>
246 ${exec_prefix}/lib/python<version>
247 Recommended locations of the directories containing the standard
248 modules.
249 ${prefix}/include/python<version>
251 ${exec_prefix}/include/python<version>
252 Recommended locations of the directories containing the include
253 files needed for developing Python extensions and embedding the
254 interpreter.
255
257 PYTHONHOME
258 Change the location of the standard Python libraries. By
259 default, the libraries are searched in ${prefix}/lib/python<ver‐
260 sion> and ${exec_prefix}/lib/python<version>, where ${prefix}
261 and ${exec_prefix} are installation-dependent directories, both
262 defaulting to /usr/local. When $PYTHONHOME is set to a single
263 directory, its value replaces both ${prefix} and ${exec_prefix}.
264 To specify different values for these, set $PYTHONHOME to ${pre‐
265 fix}:${exec_prefix}.
266 PYTHONPATH
268 Augments the default search path for module files. The format
269 is the same as the shell's $PATH: one or more directory path‐
270 names separated by colons. Non-existent directories are
271 silently ignored. The default search path is installation
272 dependent, but generally begins with ${prefix}/lib/python<ver‐
273 sion> (see PYTHONHOME above). The default search path is always
274 appended to $PYTHONPATH. If a script argument is given, the
275 directory containing the script is inserted in the path in front
276 of $PYTHONPATH. The search path can be manipulated from within
277 a Python program as the variable sys.path.
278 PYTHONSTARTUP
280 If this is the name of a readable file, the Python commands in
281 that file are executed before the first prompt is displayed in
282 interactive mode. The file is executed in the same name space
283 where interactive commands are executed so that objects defined
284 or imported in it can be used without qualification in the
285 interactive session. You can also change the prompts sys.ps1
286 and sys.ps2 in this file.
287 PYTHONOPTIMIZE
289 If this is set to a non-empty string it is equivalent to speci‐
290 fying the -O option. If set to an integer, it is equivalent to
291 specifying -O multiple times.
292 PYTHONDEBUG
294 If this is set to a non-empty string it is equivalent to speci‐
295 fying the -d option. If set to an integer, it is equivalent to
296 specifying -d multiple times.
297 PYTHONDONTWRITEBYTECODE
299 If this is set to a non-empty string it is equivalent to speci‐
300 fying the -B option (don't try to write .pyc files).
301 PYTHONINSPECT
303 If this is set to a non-empty string it is equivalent to speci‐
304 fying the -i option.
305 PYTHONIOENCODING
307 If this is set before running the interpreter, it overrides the
308 encoding used for stdin/stdout/stderr, in the syntax encoding‐
309 name:errorhandler The errorhandler part is optional and has the
310 same meaning as in str.encode. For stderr, the errorhandler
311 part is ignored; the handler will always be ´backslashreplace´.
312 PYTHONNOUSERSITE
314 If this is set to a non-empty string it is equivalent to speci‐
315 fying the -s option (Don't add the user site directory to
316 sys.path).
317 PYTHONUNBUFFERED
319 If this is set to a non-empty string it is equivalent to speci‐
320 fying the -u option.
321 PYTHONVERBOSE
323 If this is set to a non-empty string it is equivalent to speci‐
324 fying the -v option. If set to an integer, it is equivalent to
325 specifying -v multiple times.
326 PYTHONWARNINGS
328 If this is set to a comma-separated string it is equivalent to
329 specifying the -W option for each separate value.
330 PYTHONHASHSEED
332 If this variable is set to "random", a random value is used to
333 seed the hashes of str, bytes and datetime objects.
334 If PYTHONHASHSEED is set to an integer value, it is used as a
336 fixed seed for generating the hash() of the types covered by the
337 hash randomization. Its purpose is to allow repeatable hashing,
338 such as for selftests for the interpreter itself, or to allow a
339 cluster of python processes to share hash values.
340 The integer must be a decimal number in the range
342 [0,4294967295]. Specifying the value 0 will disable hash ran‐
343 domization.
344 PYTHONMALLOC
346 Set the Python memory allocators and/or install debug hooks. The
347 available memory allocators are malloc and pymalloc. The avail‐
348 able debug hooks are debug, malloc_debug, and pymalloc_debug.
349 When Python is compiled in debug mode, the default is pymal‐
351 loc_debug and the debug hooks are automatically used. Otherwise,
352 the default is pymalloc.
353 PYTHONMALLOCSTATS
355 If set to a non-empty string, Python will print statistics of
356 the pymalloc memory allocator every time a new pymalloc object
357 arena is created, and on shutdown.
358 This variable is ignored if the $PYTHONMALLOC environment vari‐
360 able is used to force the malloc(3) allocator of the C library,
361 or if Python is configured without pymalloc support.
362 PYTHONASYNCIODEBUG
364 If this environment variable is set to a non-empty string,
365 enable the debug mode of the asyncio module.
366 PYTHONTRACEMALLOC
368 If this environment variable is set to a non-empty string, start
369 tracing Python memory allocations using the tracemalloc module.
370 The value of the variable is the maximum number of frames stored
372 in a traceback of a trace. For example, PYTHONTRACEMALLOC=1
373 stores only the most recent frame.
374 PYTHONFAULTHANDLER
376 If this environment variable is set to a non-empty string,
377 faulthandler.enable() is called at startup: install a handler
378 for SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL signals to dump
379 the Python traceback.
380 This is equivalent to the -X faulthandler option.
382 PYTHONEXECUTABLE
384 If this environment variable is set, sys.argv[0] will be set to
385 its value instead of the value got through the C runtime. Only
386 works on Mac OS X.
387 PYTHONUSERBASE
389 Defines the user base directory, which is used to compute the
390 path of the user site-packages directory and Distutils installa‐
391 tion paths for python setup.py install --user.
392 PYTHONPROFILEIMPORTTIME
394 If this environment variable is set to a non-empty string,
395 Python will show how long each import takes. This is exactly
396 equivalent to setting -X importtime on the command line.
397 PYTHONBREAKPOINT
399 If this environment variable is set to 0, it disables the
400 default debugger. It can be set to the callable of your debugger
401 of choice.
402 Debug-mode variables
404 Setting these variables only has an effect in a debug build of Python,
405 that is, if Python was configured with the --with-pydebug build option.
406 PYTHONTHREADDEBUG
408 If this environment variable is set, Python will print threading
409 debug info.
410 PYTHONDUMPREFS
412 If this environment variable is set, Python will dump objects
413 and reference counts still alive after shutting down the inter‐
414 preter.
415
417 The Python Software Foundation: https://www.python.org/psf/
418
420 Main website: https://www.python.org/
421 Documentation: https://docs.python.org/
422 Developer resources: https://devguide.python.org/
423 Downloads: https://www.python.org/downloads/
424 Module repository: https://pypi.org/
425 Newsgroups: comp.lang.python, comp.lang.python.announce
426
428 Python is distributed under an Open Source license. See the file
429 "LICENSE" in the Python source distribution for information on terms &
430 conditions for accessing and otherwise using Python and for a DIS‐
431 CLAIMER OF ALL WARRANTIES.
432 PYTHON(1)