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.
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 ma‐
90 nipulations of sys.path that it entails. Also disable these ma‐
91 nipulations if site is explicitly imported later.
92 -u Force the stdout and stderr streams to be unbuffered. This op‐
94 tion 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 us‐
157 ing 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 ad‐
174 ditional 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 int_max_str_digits=number: limit the size of int<->str
202 conversions.
203 This helps avoid denial of service attacks when parsing
204 untrusted data.
205 The default is sys.int_info.default_max_str_digits. 0
206 disables.
207 -x Skip the first line of the source. This is intended for a DOS
210 specific hack only. Warning: the line numbers in error messages
211 will be off by one!
212
214 The interpreter interface resembles that of the UNIX shell: when called
215 with standard input connected to a tty device, it prompts for commands
216 and executes them until an EOF is read; when called with a file name
217 argument or with a file as standard input, it reads and executes a
218 script from that file; when called with -c command, it executes the
219 Python statement(s) given as command. Here command may contain multi‐
220 ple statements separated by newlines. Leading whitespace is signifi‐
221 cant in Python statements! In non-interactive mode, the entire input
222 is parsed before it is executed.
223 If available, the script name and additional arguments thereafter are
225 passed to the script in the Python variable sys.argv, which is a list
226 of strings (you must first import sys to be able to access it). If no
227 script name is given, sys.argv[0] is an empty string; if -c is used,
228 sys.argv[0] contains the string '-c'. Note that options interpreted by
229 the Python interpreter itself are not placed in sys.argv.
230 In interactive mode, the primary prompt is `>>>'; the second prompt
232 (which appears when a command is not complete) is `...'. The prompts
233 can be changed by assignment to sys.ps1 or sys.ps2. The interpreter
234 quits when it reads an EOF at a prompt. When an unhandled exception
235 occurs, a stack trace is printed and control returns to the primary
236 prompt; in non-interactive mode, the interpreter exits after printing
237 the stack trace. The interrupt signal raises the KeyboardInterrupt ex‐
238 ception; other UNIX signals are not caught (except that SIGPIPE is
239 sometimes ignored, in favor of the IOError exception). Error messages
240 are written to stderr.
241
243 These are subject to difference depending on local installation conven‐
244 tions; ${prefix} and ${exec_prefix} are installation-dependent and
245 should be interpreted as for GNU software; they may be the same. The
246 default for both is /usr/local.
247 ${exec_prefix}/bin/python
249 Recommended location of the interpreter.
250 ${prefix}/lib/python<version>
252 ${exec_prefix}/lib/python<version>
253 Recommended locations of the directories containing the standard
254 modules.
255 ${prefix}/include/python<version>
257 ${exec_prefix}/include/python<version>
258 Recommended locations of the directories containing the include
259 files needed for developing Python extensions and embedding the
260 interpreter.
261
263 PYTHONHOME
264 Change the location of the standard Python libraries. By de‐
265 fault, the libraries are searched in ${prefix}/lib/python<ver‐
266 sion> and ${exec_prefix}/lib/python<version>, where ${prefix}
267 and ${exec_prefix} are installation-dependent directories, both
268 defaulting to /usr/local. When $PYTHONHOME is set to a single
269 directory, its value replaces both ${prefix} and ${exec_prefix}.
270 To specify different values for these, set $PYTHONHOME to ${pre‐
271 fix}:${exec_prefix}.
272 PYTHONPATH
274 Augments the default search path for module files. The format
275 is the same as the shell's $PATH: one or more directory path‐
276 names separated by colons. Non-existent directories are
277 silently ignored. The default search path is installation de‐
278 pendent, but generally begins with ${prefix}/lib/python<version>
279 (see PYTHONHOME above). The default search path is always ap‐
280 pended to $PYTHONPATH. If a script argument is given, the di‐
281 rectory containing the script is inserted in the path in front
282 of $PYTHONPATH. The search path can be manipulated from within
283 a Python program as the variable sys.path.
284 PYTHONPLATLIBDIR
286 Override sys.platlibdir.
287 PYTHONSTARTUP
289 If this is the name of a readable file, the Python commands in
290 that file are executed before the first prompt is displayed in
291 interactive mode. The file is executed in the same name space
292 where interactive commands are executed so that objects defined
293 or imported in it can be used without qualification in the in‐
294 teractive session. You can also change the prompts sys.ps1 and
295 sys.ps2 in this file.
296 PYTHONOPTIMIZE
298 If this is set to a non-empty string it is equivalent to speci‐
299 fying the -O option. If set to an integer, it is equivalent to
300 specifying -O multiple times.
301 PYTHONDEBUG
303 If this is set to a non-empty string it is equivalent to speci‐
304 fying the -d option. If set to an integer, it is equivalent to
305 specifying -d multiple times.
306 PYTHONDONTWRITEBYTECODE
308 If this is set to a non-empty string it is equivalent to speci‐
309 fying the -B option (don't try to write .pyc files).
310 PYTHONINSPECT
312 If this is set to a non-empty string it is equivalent to speci‐
313 fying the -i option.
314 PYTHONIOENCODING
316 If this is set before running the interpreter, it overrides the
317 encoding used for stdin/stdout/stderr, in the syntax encoding‐
318 name:errorhandler The errorhandler part is optional and has the
319 same meaning as in str.encode. For stderr, the errorhandler
320 part is ignored; the handler will always be ´backslashreplace´.
321 PYTHONNOUSERSITE
323 If this is set to a non-empty string it is equivalent to speci‐
324 fying the -s option (Don't add the user site directory to
325 sys.path).
326 PYTHONUNBUFFERED
328 If this is set to a non-empty string it is equivalent to speci‐
329 fying the -u option.
330 PYTHONVERBOSE
332 If this is set to a non-empty string it is equivalent to speci‐
333 fying the -v option. If set to an integer, it is equivalent to
334 specifying -v multiple times.
335 PYTHONWARNINGS
337 If this is set to a comma-separated string it is equivalent to
338 specifying the -W option for each separate value.
339 PYTHONHASHSEED
341 If this variable is set to "random", a random value is used to
342 seed the hashes of str and bytes objects.
343 If PYTHONHASHSEED is set to an integer value, it is used as a
345 fixed seed for generating the hash() of the types covered by the
346 hash randomization. Its purpose is to allow repeatable hashing,
347 such as for selftests for the interpreter itself, or to allow a
348 cluster of python processes to share hash values.
349 The integer must be a decimal number in the range
351 [0,4294967295]. Specifying the value 0 will disable hash ran‐
352 domization.
353 PYTHONINTMAXSTRDIGITS
355 Limit the maximum digit characters in an int value when convert‐
356 ing from a string and when converting an int back to a str. A
357 value of 0 disables the limit. Conversions to or from bases 2,
358 4, 8, 16, and 32 are never limited.
359 PYTHONMALLOC
361 Set the Python memory allocators and/or install debug hooks. The
362 available memory allocators are malloc and pymalloc. The avail‐
363 able debug hooks are debug, malloc_debug, and pymalloc_debug.
364 When Python is compiled in debug mode, the default is pymal‐
366 loc_debug and the debug hooks are automatically used. Otherwise,
367 the default is pymalloc.
368 PYTHONMALLOCSTATS
370 If set to a non-empty string, Python will print statistics of
371 the pymalloc memory allocator every time a new pymalloc object
372 arena is created, and on shutdown.
373 This variable is ignored if the $PYTHONMALLOC environment vari‐
375 able is used to force the malloc(3) allocator of the C library,
376 or if Python is configured without pymalloc support.
377 PYTHONASYNCIODEBUG
379 If this environment variable is set to a non-empty string, en‐
380 able the debug mode of the asyncio module.
381 PYTHONTRACEMALLOC
383 If this environment variable is set to a non-empty string, start
384 tracing Python memory allocations using the tracemalloc module.
385 The value of the variable is the maximum number of frames stored
387 in a traceback of a trace. For example, PYTHONTRACEMALLOC=1
388 stores only the most recent frame.
389 PYTHONFAULTHANDLER
391 If this environment variable is set to a non-empty string,
392 faulthandler.enable() is called at startup: install a handler
393 for SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL signals to dump
394 the Python traceback.
395 This is equivalent to the -X faulthandler option.
397 PYTHONEXECUTABLE
399 If this environment variable is set, sys.argv[0] will be set to
400 its value instead of the value got through the C runtime. Only
401 works on Mac OS X.
402 PYTHONUSERBASE
404 Defines the user base directory, which is used to compute the
405 path of the user site-packages directory and Distutils installa‐
406 tion paths for python setup.py install --user.
407 PYTHONPROFILEIMPORTTIME
409 If this environment variable is set to a non-empty string,
410 Python will show how long each import takes. This is exactly
411 equivalent to setting -X importtime on the command line.
412 PYTHONBREAKPOINT
414 If this environment variable is set to 0, it disables the de‐
415 fault debugger. It can be set to the callable of your debugger
416 of choice.
417 Debug-mode variables
419 Setting these variables only has an effect in a debug build of Python,
420 that is, if Python was configured with the --with-pydebug build option.
421 PYTHONTHREADDEBUG
423 If this environment variable is set, Python will print threading
424 debug info.
425 PYTHONDUMPREFS
427 If this environment variable is set, Python will dump objects
428 and reference counts still alive after shutting down the inter‐
429 preter.
430
432 The Python Software Foundation: https://www.python.org/psf/
433
435 Main website: https://www.python.org/
436 Documentation: https://docs.python.org/
437 Developer resources: https://devguide.python.org/
438 Downloads: https://www.python.org/downloads/
439 Module repository: https://pypi.org/
440 Newsgroups: comp.lang.python, comp.lang.python.announce
441
443 Python is distributed under an Open Source license. See the file "LI‐
444 CENSE" in the Python source distribution for information on terms &
445 conditions for accessing and otherwise using Python and for a DIS‐
446 CLAIMER OF ALL WARRANTIES.
447 PYTHON(1)