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 showalloccount: output the total count of allocated ob‐
165 jects 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 ad‐
180 ditional 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 int_max_str_digits=number: limit the size of int<->str
208 conversions.
209 This helps avoid denial of service attacks when parsing
210 untrusted data.
211 The default is sys.int_info.default_max_str_digits. 0
212 disables.
213 -x Skip the first line of the source. This is intended for a DOS
216 specific hack only. Warning: the line numbers in error messages
217 will be off by one!
218
220 The interpreter interface resembles that of the UNIX shell: when called
221 with standard input connected to a tty device, it prompts for commands
222 and executes them until an EOF is read; when called with a file name
223 argument or with a file as standard input, it reads and executes a
224 script from that file; when called with -c command, it executes the
225 Python statement(s) given as command. Here command may contain multi‐
226 ple statements separated by newlines. Leading whitespace is signifi‐
227 cant in Python statements! In non-interactive mode, the entire input
228 is parsed before it is executed.
229 If available, the script name and additional arguments thereafter are
231 passed to the script in the Python variable sys.argv, which is a list
232 of strings (you must first import sys to be able to access it). If no
233 script name is given, sys.argv[0] is an empty string; if -c is used,
234 sys.argv[0] contains the string '-c'. Note that options interpreted by
235 the Python interpreter itself are not placed in sys.argv.
236 In interactive mode, the primary prompt is `>>>'; the second prompt
238 (which appears when a command is not complete) is `...'. The prompts
239 can be changed by assignment to sys.ps1 or sys.ps2. The interpreter
240 quits when it reads an EOF at a prompt. When an unhandled exception
241 occurs, a stack trace is printed and control returns to the primary
242 prompt; in non-interactive mode, the interpreter exits after printing
243 the stack trace. The interrupt signal raises the KeyboardInterrupt ex‐
244 ception; other UNIX signals are not caught (except that SIGPIPE is
245 sometimes ignored, in favor of the IOError exception). Error messages
246 are written to stderr.
247
249 These are subject to difference depending on local installation conven‐
250 tions; ${prefix} and ${exec_prefix} are installation-dependent and
251 should be interpreted as for GNU software; they may be the same. The
252 default for both is /usr/local.
253 ${exec_prefix}/bin/python
255 Recommended location of the interpreter.
256 ${prefix}/lib/python<version>
258 ${exec_prefix}/lib/python<version>
259 Recommended locations of the directories containing the standard
260 modules.
261 ${prefix}/include/python<version>
263 ${exec_prefix}/include/python<version>
264 Recommended locations of the directories containing the include
265 files needed for developing Python extensions and embedding the
266 interpreter.
267
269 PYTHONHOME
270 Change the location of the standard Python libraries. By de‐
271 fault, the libraries are searched in ${prefix}/lib/python<ver‐
272 sion> and ${exec_prefix}/lib/python<version>, where ${prefix}
273 and ${exec_prefix} are installation-dependent directories, both
274 defaulting to /usr/local. When $PYTHONHOME is set to a single
275 directory, its value replaces both ${prefix} and ${exec_prefix}.
276 To specify different values for these, set $PYTHONHOME to ${pre‐
277 fix}:${exec_prefix}.
278 PYTHONPATH
280 Augments the default search path for module files. The format
281 is the same as the shell's $PATH: one or more directory path‐
282 names separated by colons. Non-existent directories are
283 silently ignored. The default search path is installation de‐
284 pendent, but generally begins with ${prefix}/lib/python<version>
285 (see PYTHONHOME above). The default search path is always ap‐
286 pended to $PYTHONPATH. If a script argument is given, the di‐
287 rectory containing the script is inserted in the path in front
288 of $PYTHONPATH. The search path can be manipulated from within
289 a Python program as the variable sys.path.
290 PYTHONSTARTUP
292 If this is the name of a readable file, the Python commands in
293 that file are executed before the first prompt is displayed in
294 interactive mode. The file is executed in the same name space
295 where interactive commands are executed so that objects defined
296 or imported in it can be used without qualification in the in‐
297 teractive session. You can also change the prompts sys.ps1 and
298 sys.ps2 in this file.
299 PYTHONOPTIMIZE
301 If this is set to a non-empty string it is equivalent to speci‐
302 fying the -O option. If set to an integer, it is equivalent to
303 specifying -O multiple times.
304 PYTHONDEBUG
306 If this is set to a non-empty string it is equivalent to speci‐
307 fying the -d option. If set to an integer, it is equivalent to
308 specifying -d multiple times.
309 PYTHONDONTWRITEBYTECODE
311 If this is set to a non-empty string it is equivalent to speci‐
312 fying the -B option (don't try to write .pyc files).
313 PYTHONINSPECT
315 If this is set to a non-empty string it is equivalent to speci‐
316 fying the -i option.
317 PYTHONIOENCODING
319 If this is set before running the interpreter, it overrides the
320 encoding used for stdin/stdout/stderr, in the syntax encoding‐
321 name:errorhandler The errorhandler part is optional and has the
322 same meaning as in str.encode. For stderr, the errorhandler
323 part is ignored; the handler will always be ´backslashreplace´.
324 PYTHONNOUSERSITE
326 If this is set to a non-empty string it is equivalent to speci‐
327 fying the -s option (Don't add the user site directory to
328 sys.path).
329 PYTHONUNBUFFERED
331 If this is set to a non-empty string it is equivalent to speci‐
332 fying the -u option.
333 PYTHONVERBOSE
335 If this is set to a non-empty string it is equivalent to speci‐
336 fying the -v option. If set to an integer, it is equivalent to
337 specifying -v multiple times.
338 PYTHONWARNINGS
340 If this is set to a comma-separated string it is equivalent to
341 specifying the -W option for each separate value.
342 PYTHONHASHSEED
344 If this variable is set to "random", a random value is used to
345 seed the hashes of str and bytes objects.
346 If PYTHONHASHSEED is set to an integer value, it is used as a
348 fixed seed for generating the hash() of the types covered by the
349 hash randomization. Its purpose is to allow repeatable hashing,
350 such as for selftests for the interpreter itself, or to allow a
351 cluster of python processes to share hash values.
352 The integer must be a decimal number in the range
354 [0,4294967295]. Specifying the value 0 will disable hash ran‐
355 domization.
356 PYTHONINTMAXSTRDIGITS
358 Limit the maximum digit characters in an int value when convert‐
359 ing from a string and when converting an int back to a str. A
360 value of 0 disables the limit. Conversions to or from bases 2,
361 4, 8, 16, and 32 are never limited.
362 PYTHONMALLOC
364 Set the Python memory allocators and/or install debug hooks. The
365 available memory allocators are malloc and pymalloc. The avail‐
366 able debug hooks are debug, malloc_debug, and pymalloc_debug.
367 When Python is compiled in debug mode, the default is pymal‐
369 loc_debug and the debug hooks are automatically used. Otherwise,
370 the default is pymalloc.
371 PYTHONMALLOCSTATS
373 If set to a non-empty string, Python will print statistics of
374 the pymalloc memory allocator every time a new pymalloc object
375 arena is created, and on shutdown.
376 This variable is ignored if the $PYTHONMALLOC environment vari‐
378 able is used to force the malloc(3) allocator of the C library,
379 or if Python is configured without pymalloc support.
380 PYTHONASYNCIODEBUG
382 If this environment variable is set to a non-empty string, en‐
383 able the debug mode of the asyncio module.
384 PYTHONTRACEMALLOC
386 If this environment variable is set to a non-empty string, start
387 tracing Python memory allocations using the tracemalloc module.
388 The value of the variable is the maximum number of frames stored
390 in a traceback of a trace. For example, PYTHONTRACEMALLOC=1
391 stores only the most recent frame.
392 PYTHONFAULTHANDLER
394 If this environment variable is set to a non-empty string,
395 faulthandler.enable() is called at startup: install a handler
396 for SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL signals to dump
397 the Python traceback.
398 This is equivalent to the -X faulthandler option.
400 PYTHONEXECUTABLE
402 If this environment variable is set, sys.argv[0] will be set to
403 its value instead of the value got through the C runtime. Only
404 works on Mac OS X.
405 PYTHONUSERBASE
407 Defines the user base directory, which is used to compute the
408 path of the user site-packages directory and Distutils installa‐
409 tion paths for python setup.py install --user.
410 PYTHONPROFILEIMPORTTIME
412 If this environment variable is set to a non-empty string,
413 Python will show how long each import takes. This is exactly
414 equivalent to setting -X importtime on the command line.
415 PYTHONBREAKPOINT
417 If this environment variable is set to 0, it disables the de‐
418 fault debugger. It can be set to the callable of your debugger
419 of choice.
420 Debug-mode variables
422 Setting these variables only has an effect in a debug build of Python,
423 that is, if Python was configured with the --with-pydebug build option.
424 PYTHONTHREADDEBUG
426 If this environment variable is set, Python will print threading
427 debug info.
428 PYTHONDUMPREFS
430 If this environment variable is set, Python will dump objects
431 and reference counts still alive after shutting down the inter‐
432 preter.
433
435 The Python Software Foundation: https://www.python.org/psf/
436
438 Main website: https://www.python.org/
439 Documentation: https://docs.python.org/
440 Developer resources: https://devguide.python.org/
441 Downloads: https://www.python.org/downloads/
442 Module repository: https://pypi.org/
443 Newsgroups: comp.lang.python, comp.lang.python.announce
444
446 Python is distributed under an Open Source license. See the file "LI‐
447 CENSE" in the Python source distribution for information on terms &
448 conditions for accessing and otherwise using Python and for a DIS‐
449 CLAIMER OF ALL WARRANTIES.
450 PYTHON(1)