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() C function
204 * Enable the faulthandler module to dump the Python
205 traceback on a crash
206 * Enable asyncio debug mode
207 * Set the dev_mode attribute of sys.flags to True
208 * io.IOBase destructor logs close() exceptions
209 -X utf8: enable UTF-8 mode for operating system interfaces,
211 overriding the default
212 locale-aware mode. -X utf8=0 explicitly disables UTF-8
213 mode (even when it would
214 otherwise activate automatically). See PYTHONUTF8 for
215 more details
216 -X pycache_prefix=PATH: enable writing .pyc files to a par‐
218 allel tree rooted at the
219 given directory instead of to the code tree.
220 -x Skip the first line of the source. This is intended for a DOS
222 specific hack only. Warning: the line numbers in error messages
223 will be off by one!
224
226 The interpreter interface resembles that of the UNIX shell: when called
227 with standard input connected to a tty device, it prompts for commands
228 and executes them until an EOF is read; when called with a file name
229 argument or with a file as standard input, it reads and executes a
230 script from that file; when called with -c command, it executes the
231 Python statement(s) given as command. Here command may contain multi‐
232 ple statements separated by newlines. Leading whitespace is signifi‐
233 cant in Python statements! In non-interactive mode, the entire input
234 is parsed before it is executed.
235 If available, the script name and additional arguments thereafter are
237 passed to the script in the Python variable sys.argv, which is a list
238 of strings (you must first import sys to be able to access it). If no
239 script name is given, sys.argv[0] is an empty string; if -c is used,
240 sys.argv[0] contains the string '-c'. Note that options interpreted by
241 the Python interpreter itself are not placed in sys.argv.
242 In interactive mode, the primary prompt is `>>>'; the second prompt
244 (which appears when a command is not complete) is `...'. The prompts
245 can be changed by assignment to sys.ps1 or sys.ps2. The interpreter
246 quits when it reads an EOF at a prompt. When an unhandled exception
247 occurs, a stack trace is printed and control returns to the primary
248 prompt; in non-interactive mode, the interpreter exits after printing
249 the stack trace. The interrupt signal raises the KeyboardInterrupt ex‐
250 ception; other UNIX signals are not caught (except that SIGPIPE is
251 sometimes ignored, in favor of the IOError exception). Error messages
252 are written to stderr.
253
255 These are subject to difference depending on local installation conven‐
256 tions; ${prefix} and ${exec_prefix} are installation-dependent and
257 should be interpreted as for GNU software; they may be the same. The
258 default for both is /usr/local.
259 ${exec_prefix}/bin/python
261 Recommended location of the interpreter.
262 ${prefix}/lib/python<version>
264 ${exec_prefix}/lib/python<version>
265 Recommended locations of the directories containing the standard
266 modules.
267 ${prefix}/include/python<version>
269 ${exec_prefix}/include/python<version>
270 Recommended locations of the directories containing the include
271 files needed for developing Python extensions and embedding the
272 interpreter.
273
275 PYTHONHOME
276 Change the location of the standard Python libraries. By de‐
277 fault, the libraries are searched in ${prefix}/lib/python<ver‐
278 sion> and ${exec_prefix}/lib/python<version>, where ${prefix}
279 and ${exec_prefix} are installation-dependent directories, both
280 defaulting to /usr/local. When $PYTHONHOME is set to a single
281 directory, its value replaces both ${prefix} and ${exec_prefix}.
282 To specify different values for these, set $PYTHONHOME to ${pre‐
283 fix}:${exec_prefix}.
284 PYTHONPATH
286 Augments the default search path for module files. The format
287 is the same as the shell's $PATH: one or more directory path‐
288 names separated by colons. Non-existent directories are
289 silently ignored. The default search path is installation de‐
290 pendent, but generally begins with ${prefix}/lib/python<version>
291 (see PYTHONHOME above). The default search path is always ap‐
292 pended to $PYTHONPATH. If a script argument is given, the di‐
293 rectory containing the script is inserted in the path in front
294 of $PYTHONPATH. The search path can be manipulated from within
295 a Python program as the variable sys.path.
296 PYTHONPLATLIBDIR
298 Override sys.platlibdir.
299 PYTHONSTARTUP
301 If this is the name of a readable file, the Python commands in
302 that file are executed before the first prompt is displayed in
303 interactive mode. The file is executed in the same name space
304 where interactive commands are executed so that objects defined
305 or imported in it can be used without qualification in the in‐
306 teractive session. You can also change the prompts sys.ps1 and
307 sys.ps2 in this file.
308 PYTHONOPTIMIZE
310 If this is set to a non-empty string it is equivalent to speci‐
311 fying the -O option. If set to an integer, it is equivalent to
312 specifying -O multiple times.
313 PYTHONDEBUG
315 If this is set to a non-empty string it is equivalent to speci‐
316 fying the -d option. If set to an integer, it is equivalent to
317 specifying -d multiple times.
318 PYTHONDONTWRITEBYTECODE
320 If this is set to a non-empty string it is equivalent to speci‐
321 fying the -B option (don't try to write .pyc files).
322 PYTHONINSPECT
324 If this is set to a non-empty string it is equivalent to speci‐
325 fying the -i option.
326 PYTHONIOENCODING
328 If this is set before running the interpreter, it overrides the
329 encoding used for stdin/stdout/stderr, in the syntax encoding‐
330 name:errorhandler The errorhandler part is optional and has the
331 same meaning as in str.encode. For stderr, the errorhandler
332 part is ignored; the handler will always be ´backslashreplace´.
333 PYTHONNOUSERSITE
335 If this is set to a non-empty string it is equivalent to speci‐
336 fying the -s option (Don't add the user site directory to
337 sys.path).
338 PYTHONUNBUFFERED
340 If this is set to a non-empty string it is equivalent to speci‐
341 fying the -u option.
342 PYTHONVERBOSE
344 If this is set to a non-empty string it is equivalent to speci‐
345 fying the -v option. If set to an integer, it is equivalent to
346 specifying -v multiple times.
347 PYTHONWARNINGS
349 If this is set to a comma-separated string it is equivalent to
350 specifying the -W option for each separate value.
351 PYTHONHASHSEED
353 If this variable is set to "random", a random value is used to
354 seed the hashes of str and bytes objects.
355 If PYTHONHASHSEED is set to an integer value, it is used as a
357 fixed seed for generating the hash() of the types covered by the
358 hash randomization. Its purpose is to allow repeatable hashing,
359 such as for selftests for the interpreter itself, or to allow a
360 cluster of python processes to share hash values.
361 The integer must be a decimal number in the range
363 [0,4294967295]. Specifying the value 0 will disable hash ran‐
364 domization.
365 PYTHONMALLOC
367 Set the Python memory allocators and/or install debug hooks. The
368 available memory allocators are malloc and pymalloc. The avail‐
369 able debug hooks are debug, malloc_debug, and pymalloc_debug.
370 When Python is compiled in debug mode, the default is pymal‐
372 loc_debug and the debug hooks are automatically used. Otherwise,
373 the default is pymalloc.
374 PYTHONMALLOCSTATS
376 If set to a non-empty string, Python will print statistics of
377 the pymalloc memory allocator every time a new pymalloc object
378 arena is created, and on shutdown.
379 This variable is ignored if the $PYTHONMALLOC environment vari‐
381 able is used to force the malloc(3) allocator of the C library,
382 or if Python is configured without pymalloc support.
383 PYTHONASYNCIODEBUG
385 If this environment variable is set to a non-empty string, en‐
386 able the debug mode of the asyncio module.
387 PYTHONTRACEMALLOC
389 If this environment variable is set to a non-empty string, start
390 tracing Python memory allocations using the tracemalloc module.
391 The value of the variable is the maximum number of frames stored
393 in a traceback of a trace. For example, PYTHONTRACEMALLOC=1
394 stores only the most recent frame.
395 PYTHONFAULTHANDLER
397 If this environment variable is set to a non-empty string,
398 faulthandler.enable() is called at startup: install a handler
399 for SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL signals to dump
400 the Python traceback.
401 This is equivalent to the -X faulthandler option.
403 PYTHONEXECUTABLE
405 If this environment variable is set, sys.argv[0] will be set to
406 its value instead of the value got through the C runtime. Only
407 works on Mac OS X.
408 PYTHONUSERBASE
410 Defines the user base directory, which is used to compute the
411 path of the user site-packages directory and Distutils installa‐
412 tion paths for python setup.py install --user.
413 PYTHONPROFILEIMPORTTIME
415 If this environment variable is set to a non-empty string,
416 Python will show how long each import takes. This is exactly
417 equivalent to setting -X importtime on the command line.
418 PYTHONBREAKPOINT
420 If this environment variable is set to 0, it disables the de‐
421 fault debugger. It can be set to the callable of your debugger
422 of choice.
423 Debug-mode variables
425 Setting these variables only has an effect in a debug build of Python,
426 that is, if Python was configured with the --with-pydebug build option.
427 PYTHONTHREADDEBUG
429 If this environment variable is set, Python will print threading
430 debug info.
431 PYTHONDUMPREFS
433 If this environment variable is set, Python will dump objects
434 and reference counts still alive after shutting down the inter‐
435 preter.
436
438 The Python Software Foundation: https://www.python.org/psf/
439
441 Main website: https://www.python.org/
442 Documentation: https://docs.python.org/
443 Developer resources: https://devguide.python.org/
444 Downloads: https://www.python.org/downloads/
445 Module repository: https://pypi.org/
446 Newsgroups: comp.lang.python, comp.lang.python.announce
447
449 Python is distributed under an Open Source license. See the file "LI‐
450 CENSE" in the Python source distribution for information on terms &
451 conditions for accessing and otherwise using Python and for a DIS‐
452 CLAIMER OF ALL WARRANTIES.
453 PYTHON(1)