Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1 | :mod:`sys` --- System-specific parameters and functions |
| 2 | ======================================================= |
| 3 | |
| 4 | .. module:: sys |
| 5 | :synopsis: Access system-specific parameters and functions. |
| 6 | |
| 7 | |
| 8 | This module provides access to some variables used or maintained by the |
| 9 | interpreter and to functions that interact strongly with the interpreter. It is |
| 10 | always available. |
| 11 | |
| 12 | |
Barry Warsaw | a40453d | 2010-10-16 14:17:50 +0000 | [diff] [blame] | 13 | .. data:: abiflags |
| 14 | |
| 15 | On POSIX systems where Python is build with the standard ``configure`` |
| 16 | script, this contains the ABI flags as specified by :pep:`3149`. |
| 17 | |
| 18 | .. versionadded:: 3.2 |
| 19 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 20 | .. data:: argv |
| 21 | |
| 22 | The list of command line arguments passed to a Python script. ``argv[0]`` is the |
| 23 | script name (it is operating system dependent whether this is a full pathname or |
| 24 | not). If the command was executed using the :option:`-c` command line option to |
| 25 | the interpreter, ``argv[0]`` is set to the string ``'-c'``. If no script name |
| 26 | was passed to the Python interpreter, ``argv[0]`` is the empty string. |
| 27 | |
| 28 | To loop over the standard input, or the list of files given on the |
| 29 | command line, see the :mod:`fileinput` module. |
| 30 | |
| 31 | |
Vinay Sajip | 7ded1f0 | 2012-05-26 03:45:29 +0100 | [diff] [blame^] | 32 | .. data:: base_exec_prefix |
| 33 | |
| 34 | Set during Python startup, before ``site.py`` is run, to the same value as |
| 35 | :data:`exec_prefix`. If not running in a virtual environment, the values |
| 36 | will stay the same; if ``site.py`` finds that a virtual environment is in |
| 37 | use, the values of :data:`prefix` and :data:`exec_prefix` will be changed to |
| 38 | point to the virtual environment, whereas :data:`base_prefix` and |
| 39 | :data:`base_exec_prefix` will remain pointing to the base Python |
| 40 | installation (the one which the virtual environment was created from). |
| 41 | |
| 42 | .. data:: base_prefix |
| 43 | |
| 44 | Set during Python startup, before ``site.py`` is run, to the same value as |
| 45 | :data:`prefix`. If not running in a virtual environment, the values |
| 46 | will stay the same; if ``site.py`` finds that a virtual environment is in |
| 47 | use, the values of :data:`prefix` and :data:`exec_prefix` will be changed to |
| 48 | point to the virtual environment, whereas :data:`base_prefix` and |
| 49 | :data:`base_exec_prefix` will remain pointing to the base Python |
| 50 | installation (the one which the virtual environment was created from). |
| 51 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 52 | .. data:: byteorder |
| 53 | |
| 54 | An indicator of the native byte order. This will have the value ``'big'`` on |
| 55 | big-endian (most-significant byte first) platforms, and ``'little'`` on |
| 56 | little-endian (least-significant byte first) platforms. |
| 57 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 58 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 59 | .. data:: builtin_module_names |
| 60 | |
| 61 | A tuple of strings giving the names of all modules that are compiled into this |
| 62 | Python interpreter. (This information is not available in any other way --- |
| 63 | ``modules.keys()`` only lists the imported modules.) |
| 64 | |
| 65 | |
Georg Brandl | 8527126 | 2010-10-17 11:06:14 +0000 | [diff] [blame] | 66 | .. function:: call_tracing(func, args) |
| 67 | |
| 68 | Call ``func(*args)``, while tracing is enabled. The tracing state is saved, |
| 69 | and restored afterwards. This is intended to be called from a debugger from |
| 70 | a checkpoint, to recursively debug some other code. |
| 71 | |
| 72 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 73 | .. data:: copyright |
| 74 | |
| 75 | A string containing the copyright pertaining to the Python interpreter. |
| 76 | |
| 77 | |
Christian Heimes | 15ebc88 | 2008-02-04 18:48:49 +0000 | [diff] [blame] | 78 | .. function:: _clear_type_cache() |
| 79 | |
| 80 | Clear the internal type cache. The type cache is used to speed up attribute |
| 81 | and method lookups. Use the function *only* to drop unnecessary references |
| 82 | during reference leak debugging. |
| 83 | |
| 84 | This function should be used for internal and specialized purposes only. |
Christian Heimes | 2685563 | 2008-01-27 23:50:43 +0000 | [diff] [blame] | 85 | |
Christian Heimes | 2685563 | 2008-01-27 23:50:43 +0000 | [diff] [blame] | 86 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 87 | .. function:: _current_frames() |
| 88 | |
| 89 | Return a dictionary mapping each thread's identifier to the topmost stack frame |
| 90 | currently active in that thread at the time the function is called. Note that |
| 91 | functions in the :mod:`traceback` module can build the call stack given such a |
| 92 | frame. |
| 93 | |
| 94 | This is most useful for debugging deadlock: this function does not require the |
| 95 | deadlocked threads' cooperation, and such threads' call stacks are frozen for as |
| 96 | long as they remain deadlocked. The frame returned for a non-deadlocked thread |
| 97 | may bear no relationship to that thread's current activity by the time calling |
| 98 | code examines the frame. |
| 99 | |
| 100 | This function should be used for internal and specialized purposes only. |
| 101 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 102 | |
| 103 | .. data:: dllhandle |
| 104 | |
| 105 | Integer specifying the handle of the Python DLL. Availability: Windows. |
| 106 | |
| 107 | |
| 108 | .. function:: displayhook(value) |
| 109 | |
Victor Stinner | 13d49ee | 2010-12-04 17:24:33 +0000 | [diff] [blame] | 110 | If *value* is not ``None``, this function prints ``repr(value)`` to |
| 111 | ``sys.stdout``, and saves *value* in ``builtins._``. If ``repr(value)`` is |
| 112 | not encodable to ``sys.stdout.encoding`` with ``sys.stdout.errors`` error |
| 113 | handler (which is probably ``'strict'``), encode it to |
| 114 | ``sys.stdout.encoding`` with ``'backslashreplace'`` error handler. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 115 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 116 | ``sys.displayhook`` is called on the result of evaluating an :term:`expression` |
| 117 | entered in an interactive Python session. The display of these values can be |
| 118 | customized by assigning another one-argument function to ``sys.displayhook``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 119 | |
Victor Stinner | 13d49ee | 2010-12-04 17:24:33 +0000 | [diff] [blame] | 120 | Pseudo-code:: |
| 121 | |
| 122 | def displayhook(value): |
| 123 | if value is None: |
| 124 | return |
| 125 | # Set '_' to None to avoid recursion |
| 126 | builtins._ = None |
| 127 | text = repr(value) |
| 128 | try: |
| 129 | sys.stdout.write(text) |
| 130 | except UnicodeEncodeError: |
| 131 | bytes = text.encode(sys.stdout.encoding, 'backslashreplace') |
| 132 | if hasattr(sys.stdout, 'buffer'): |
| 133 | sys.stdout.buffer.write(bytes) |
| 134 | else: |
| 135 | text = bytes.decode(sys.stdout.encoding, 'strict') |
| 136 | sys.stdout.write(text) |
| 137 | sys.stdout.write("\n") |
| 138 | builtins._ = value |
| 139 | |
| 140 | .. versionchanged:: 3.2 |
| 141 | Use ``'backslashreplace'`` error handler on :exc:`UnicodeEncodeError`. |
| 142 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 143 | |
Éric Araujo | da27263 | 2011-10-05 01:17:38 +0200 | [diff] [blame] | 144 | .. data:: dont_write_bytecode |
| 145 | |
| 146 | If this is true, Python won't try to write ``.pyc`` or ``.pyo`` files on the |
| 147 | import of source modules. This value is initially set to ``True`` or |
| 148 | ``False`` depending on the :option:`-B` command line option and the |
| 149 | :envvar:`PYTHONDONTWRITEBYTECODE` environment variable, but you can set it |
| 150 | yourself to control bytecode file generation. |
| 151 | |
| 152 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 153 | .. function:: excepthook(type, value, traceback) |
| 154 | |
| 155 | This function prints out a given traceback and exception to ``sys.stderr``. |
| 156 | |
| 157 | When an exception is raised and uncaught, the interpreter calls |
| 158 | ``sys.excepthook`` with three arguments, the exception class, exception |
| 159 | instance, and a traceback object. In an interactive session this happens just |
| 160 | before control is returned to the prompt; in a Python program this happens just |
| 161 | before the program exits. The handling of such top-level exceptions can be |
| 162 | customized by assigning another three-argument function to ``sys.excepthook``. |
| 163 | |
| 164 | |
| 165 | .. data:: __displayhook__ |
| 166 | __excepthook__ |
| 167 | |
| 168 | These objects contain the original values of ``displayhook`` and ``excepthook`` |
| 169 | at the start of the program. They are saved so that ``displayhook`` and |
| 170 | ``excepthook`` can be restored in case they happen to get replaced with broken |
| 171 | objects. |
| 172 | |
| 173 | |
| 174 | .. function:: exc_info() |
| 175 | |
| 176 | This function returns a tuple of three values that give information about the |
| 177 | exception that is currently being handled. The information returned is specific |
| 178 | both to the current thread and to the current stack frame. If the current stack |
| 179 | frame is not handling an exception, the information is taken from the calling |
| 180 | stack frame, or its caller, and so on until a stack frame is found that is |
| 181 | handling an exception. Here, "handling an exception" is defined as "executing |
Benjamin Peterson | eec3d71 | 2008-06-11 15:59:43 +0000 | [diff] [blame] | 182 | an except clause." For any stack frame, only information about the exception |
| 183 | being currently handled is accessible. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 184 | |
| 185 | .. index:: object: traceback |
| 186 | |
Georg Brandl | 482b151 | 2010-03-21 09:02:59 +0000 | [diff] [blame] | 187 | If no exception is being handled anywhere on the stack, a tuple containing |
| 188 | three ``None`` values is returned. Otherwise, the values returned are |
| 189 | ``(type, value, traceback)``. Their meaning is: *type* gets the type of the |
| 190 | exception being handled (a subclass of :exc:`BaseException`); *value* gets |
| 191 | the exception instance (an instance of the exception type); *traceback* gets |
| 192 | a traceback object (see the Reference Manual) which encapsulates the call |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 193 | stack at the point where the exception originally occurred. |
| 194 | |
| 195 | .. warning:: |
| 196 | |
Georg Brandl | e6bcc91 | 2008-05-12 18:05:20 +0000 | [diff] [blame] | 197 | Assigning the *traceback* return value to a local variable in a function |
| 198 | that is handling an exception will cause a circular reference. Since most |
| 199 | functions don't need access to the traceback, the best solution is to use |
| 200 | something like ``exctype, value = sys.exc_info()[:2]`` to extract only the |
| 201 | exception type and value. If you do need the traceback, make sure to |
| 202 | delete it after use (best done with a :keyword:`try` |
| 203 | ... :keyword:`finally` statement) or to call :func:`exc_info` in a |
| 204 | function that does not itself handle an exception. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 205 | |
Georg Brandl | e6bcc91 | 2008-05-12 18:05:20 +0000 | [diff] [blame] | 206 | Such cycles are normally automatically reclaimed when garbage collection |
| 207 | is enabled and they become unreachable, but it remains more efficient to |
| 208 | avoid creating cycles. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 209 | |
| 210 | |
| 211 | .. data:: exec_prefix |
| 212 | |
| 213 | A string giving the site-specific directory prefix where the platform-dependent |
| 214 | Python files are installed; by default, this is also ``'/usr/local'``. This can |
Éric Araujo | 713d303 | 2010-11-18 16:38:46 +0000 | [diff] [blame] | 215 | be set at build time with the ``--exec-prefix`` argument to the |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 216 | :program:`configure` script. Specifically, all configuration files (e.g. the |
Éric Araujo | 58a9153 | 2011-10-05 01:28:24 +0200 | [diff] [blame] | 217 | :file:`pyconfig.h` header file) are installed in the directory |
Georg Brandl | eb25fb7 | 2012-02-23 21:12:39 +0100 | [diff] [blame] | 218 | :file:`{exec_prefix}/lib/python{X.Y}/config`, and shared library modules are |
Éric Araujo | 58a9153 | 2011-10-05 01:28:24 +0200 | [diff] [blame] | 219 | installed in :file:`{exec_prefix}/lib/python{X.Y}/lib-dynload`, where *X.Y* |
| 220 | is the version number of Python, for example ``3.2``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 221 | |
Vinay Sajip | 7ded1f0 | 2012-05-26 03:45:29 +0100 | [diff] [blame^] | 222 | .. note:: If a virtual environment is in effect, this value will be changed |
| 223 | in ``site.py`` to point to the virtual environment. The value for the |
| 224 | Python installation will still be available, via :data:`base_exec_prefix`. |
| 225 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 226 | |
| 227 | .. data:: executable |
| 228 | |
Petri Lehtinen | 9713321 | 2012-02-02 20:59:48 +0200 | [diff] [blame] | 229 | A string giving the absolute path of the executable binary for the Python |
| 230 | interpreter, on systems where this makes sense. If Python is unable to retrieve |
| 231 | the real path to its executable, :data:`sys.executable` will be an empty string |
| 232 | or ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 233 | |
| 234 | |
| 235 | .. function:: exit([arg]) |
| 236 | |
| 237 | Exit from Python. This is implemented by raising the :exc:`SystemExit` |
| 238 | exception, so cleanup actions specified by finally clauses of :keyword:`try` |
Georg Brandl | 6f4e68d | 2010-10-17 10:51:45 +0000 | [diff] [blame] | 239 | statements are honored, and it is possible to intercept the exit attempt at |
| 240 | an outer level. |
| 241 | |
| 242 | The optional argument *arg* can be an integer giving the exit status |
| 243 | (defaulting to zero), or another type of object. If it is an integer, zero |
| 244 | is considered "successful termination" and any nonzero value is considered |
| 245 | "abnormal termination" by shells and the like. Most systems require it to be |
| 246 | in the range 0-127, and produce undefined results otherwise. Some systems |
| 247 | have a convention for assigning specific meanings to specific exit codes, but |
| 248 | these are generally underdeveloped; Unix programs generally use 2 for command |
| 249 | line syntax errors and 1 for all other kind of errors. If another type of |
| 250 | object is passed, ``None`` is equivalent to passing zero, and any other |
| 251 | object is printed to :data:`stderr` and results in an exit code of 1. In |
| 252 | particular, ``sys.exit("some error message")`` is a quick way to exit a |
| 253 | program when an error occurs. |
| 254 | |
| 255 | Since :func:`exit` ultimately "only" raises an exception, it will only exit |
| 256 | the process when called from the main thread, and the exception is not |
| 257 | intercepted. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 258 | |
| 259 | |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 260 | .. data:: flags |
| 261 | |
Benjamin Peterson | 2b8ef2d | 2011-04-20 18:31:22 -0500 | [diff] [blame] | 262 | The :term:`struct sequence` *flags* exposes the status of command line |
| 263 | flags. The attributes are read only. |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 264 | |
Éric Araujo | 5ab4776 | 2011-03-26 00:47:04 +0100 | [diff] [blame] | 265 | ============================= ============================= |
| 266 | attribute flag |
| 267 | ============================= ============================= |
| 268 | :const:`debug` :option:`-d` |
Éric Araujo | 5ab4776 | 2011-03-26 00:47:04 +0100 | [diff] [blame] | 269 | :const:`inspect` :option:`-i` |
| 270 | :const:`interactive` :option:`-i` |
| 271 | :const:`optimize` :option:`-O` or :option:`-OO` |
| 272 | :const:`dont_write_bytecode` :option:`-B` |
| 273 | :const:`no_user_site` :option:`-s` |
| 274 | :const:`no_site` :option:`-S` |
| 275 | :const:`ignore_environment` :option:`-E` |
| 276 | :const:`verbose` :option:`-v` |
| 277 | :const:`bytes_warning` :option:`-b` |
Éric Araujo | 722bec4 | 2011-03-26 01:59:47 +0100 | [diff] [blame] | 278 | :const:`quiet` :option:`-q` |
Georg Brandl | 2daf6ae | 2012-02-20 19:54:16 +0100 | [diff] [blame] | 279 | :const:`hash_randomization` :option:`-R` |
Éric Araujo | 5ab4776 | 2011-03-26 00:47:04 +0100 | [diff] [blame] | 280 | ============================= ============================= |
Georg Brandl | 8aa7e99 | 2010-12-28 18:30:18 +0000 | [diff] [blame] | 281 | |
| 282 | .. versionchanged:: 3.2 |
| 283 | Added ``quiet`` attribute for the new :option:`-q` flag. |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 284 | |
Georg Brandl | 09a7c72 | 2012-02-20 21:31:46 +0100 | [diff] [blame] | 285 | .. versionadded:: 3.2.3 |
Georg Brandl | 2daf6ae | 2012-02-20 19:54:16 +0100 | [diff] [blame] | 286 | The ``hash_randomization`` attribute. |
| 287 | |
Éric Araujo | 3e89870 | 2011-04-24 04:37:00 +0200 | [diff] [blame] | 288 | .. versionchanged:: 3.3 |
| 289 | Removed obsolete ``division_warning`` attribute. |
| 290 | |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 291 | |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 292 | .. data:: float_info |
| 293 | |
Benjamin Peterson | 2b8ef2d | 2011-04-20 18:31:22 -0500 | [diff] [blame] | 294 | A :term:`struct sequence` holding information about the float type. It |
| 295 | contains low level information about the precision and internal |
| 296 | representation. The values correspond to the various floating-point |
| 297 | constants defined in the standard header file :file:`float.h` for the 'C' |
| 298 | programming language; see section 5.2.4.2.2 of the 1999 ISO/IEC C standard |
| 299 | [C99]_, 'Characteristics of floating types', for details. |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 300 | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 301 | +---------------------+----------------+--------------------------------------------------+ |
| 302 | | attribute | float.h macro | explanation | |
| 303 | +=====================+================+==================================================+ |
Mark Dickinson | 39af05f | 2010-07-03 09:17:16 +0000 | [diff] [blame] | 304 | | :const:`epsilon` | DBL_EPSILON | difference between 1 and the least value greater | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 305 | | | | than 1 that is representable as a float | |
| 306 | +---------------------+----------------+--------------------------------------------------+ |
| 307 | | :const:`dig` | DBL_DIG | maximum number of decimal digits that can be | |
| 308 | | | | faithfully represented in a float; see below | |
| 309 | +---------------------+----------------+--------------------------------------------------+ |
| 310 | | :const:`mant_dig` | DBL_MANT_DIG | float precision: the number of base-``radix`` | |
| 311 | | | | digits in the significand of a float | |
| 312 | +---------------------+----------------+--------------------------------------------------+ |
| 313 | | :const:`max` | DBL_MAX | maximum representable finite float | |
| 314 | +---------------------+----------------+--------------------------------------------------+ |
| 315 | | :const:`max_exp` | DBL_MAX_EXP | maximum integer e such that ``radix**(e-1)`` is | |
| 316 | | | | a representable finite float | |
| 317 | +---------------------+----------------+--------------------------------------------------+ |
| 318 | | :const:`max_10_exp` | DBL_MAX_10_EXP | maximum integer e such that ``10**e`` is in the | |
| 319 | | | | range of representable finite floats | |
| 320 | +---------------------+----------------+--------------------------------------------------+ |
| 321 | | :const:`min` | DBL_MIN | minimum positive normalized float | |
| 322 | +---------------------+----------------+--------------------------------------------------+ |
| 323 | | :const:`min_exp` | DBL_MIN_EXP | minimum integer e such that ``radix**(e-1)`` is | |
| 324 | | | | a normalized float | |
| 325 | +---------------------+----------------+--------------------------------------------------+ |
| 326 | | :const:`min_10_exp` | DBL_MIN_10_EXP | minimum integer e such that ``10**e`` is a | |
| 327 | | | | normalized float | |
| 328 | +---------------------+----------------+--------------------------------------------------+ |
| 329 | | :const:`radix` | FLT_RADIX | radix of exponent representation | |
| 330 | +---------------------+----------------+--------------------------------------------------+ |
Mark Dickinson | b1e58fe | 2011-11-19 16:26:45 +0000 | [diff] [blame] | 331 | | :const:`rounds` | FLT_ROUNDS | integer constant representing the rounding mode | |
| 332 | | | | used for arithmetic operations. This reflects | |
| 333 | | | | the value of the system FLT_ROUNDS macro at | |
| 334 | | | | interpreter startup time. See section 5.2.4.2.2 | |
| 335 | | | | of the C99 standard for an explanation of the | |
| 336 | | | | possible values and their meanings. | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 337 | +---------------------+----------------+--------------------------------------------------+ |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 338 | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 339 | The attribute :attr:`sys.float_info.dig` needs further explanation. If |
| 340 | ``s`` is any string representing a decimal number with at most |
| 341 | :attr:`sys.float_info.dig` significant digits, then converting ``s`` to a |
| 342 | float and back again will recover a string representing the same decimal |
| 343 | value:: |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 344 | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 345 | >>> import sys |
| 346 | >>> sys.float_info.dig |
| 347 | 15 |
| 348 | >>> s = '3.14159265358979' # decimal string with 15 significant digits |
| 349 | >>> format(float(s), '.15g') # convert to float and back -> same value |
| 350 | '3.14159265358979' |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 351 | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 352 | But for strings with more than :attr:`sys.float_info.dig` significant digits, |
| 353 | this isn't always true:: |
| 354 | |
| 355 | >>> s = '9876543211234567' # 16 significant digits is too many! |
| 356 | >>> format(float(s), '.16g') # conversion changes value |
| 357 | '9876543211234568' |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 358 | |
Mark Dickinson | b08a53a | 2009-04-16 19:52:09 +0000 | [diff] [blame] | 359 | .. data:: float_repr_style |
| 360 | |
| 361 | A string indicating how the :func:`repr` function behaves for |
| 362 | floats. If the string has value ``'short'`` then for a finite |
| 363 | float ``x``, ``repr(x)`` aims to produce a short string with the |
| 364 | property that ``float(repr(x)) == x``. This is the usual behaviour |
| 365 | in Python 3.1 and later. Otherwise, ``float_repr_style`` has value |
| 366 | ``'legacy'`` and ``repr(x)`` behaves in the same way as it did in |
| 367 | versions of Python prior to 3.1. |
| 368 | |
| 369 | .. versionadded:: 3.1 |
| 370 | |
| 371 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 372 | .. function:: getcheckinterval() |
| 373 | |
| 374 | Return the interpreter's "check interval"; see :func:`setcheckinterval`. |
| 375 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 376 | .. deprecated:: 3.2 |
| 377 | Use :func:`getswitchinterval` instead. |
| 378 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 379 | |
| 380 | .. function:: getdefaultencoding() |
| 381 | |
| 382 | Return the name of the current default string encoding used by the Unicode |
| 383 | implementation. |
| 384 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 385 | |
| 386 | .. function:: getdlopenflags() |
| 387 | |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 388 | Return the current value of the flags that are used for :c:func:`dlopen` calls. |
Neal Norwitz | 6cf49cf | 2008-03-24 06:22:57 +0000 | [diff] [blame] | 389 | The flag constants are defined in the :mod:`ctypes` and :mod:`DLFCN` modules. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 390 | Availability: Unix. |
| 391 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 392 | |
| 393 | .. function:: getfilesystemencoding() |
| 394 | |
Victor Stinner | b744ba1 | 2010-05-15 12:27:16 +0000 | [diff] [blame] | 395 | Return the name of the encoding used to convert Unicode filenames into |
| 396 | system file names. The result value depends on the operating system: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 397 | |
Ezio Melotti | d5334e1 | 2010-04-29 16:24:51 +0000 | [diff] [blame] | 398 | * On Mac OS X, the encoding is ``'utf-8'``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 399 | |
| 400 | * On Unix, the encoding is the user's preference according to the result of |
Victor Stinner | b744ba1 | 2010-05-15 12:27:16 +0000 | [diff] [blame] | 401 | nl_langinfo(CODESET), or ``'utf-8'`` if ``nl_langinfo(CODESET)`` failed. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 402 | |
| 403 | * On Windows NT+, file names are Unicode natively, so no conversion is |
Ezio Melotti | d5334e1 | 2010-04-29 16:24:51 +0000 | [diff] [blame] | 404 | performed. :func:`getfilesystemencoding` still returns ``'mbcs'``, as |
| 405 | this is the encoding that applications should use when they explicitly |
| 406 | want to convert Unicode strings to byte strings that are equivalent when |
| 407 | used as file names. |
| 408 | |
| 409 | * On Windows 9x, the encoding is ``'mbcs'``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 410 | |
Victor Stinner | b744ba1 | 2010-05-15 12:27:16 +0000 | [diff] [blame] | 411 | .. versionchanged:: 3.2 |
| 412 | On Unix, use ``'utf-8'`` instead of ``None`` if ``nl_langinfo(CODESET)`` |
| 413 | failed. :func:`getfilesystemencoding` result cannot be ``None``. |
| 414 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 415 | |
| 416 | .. function:: getrefcount(object) |
| 417 | |
| 418 | Return the reference count of the *object*. The count returned is generally one |
| 419 | higher than you might expect, because it includes the (temporary) reference as |
| 420 | an argument to :func:`getrefcount`. |
| 421 | |
| 422 | |
| 423 | .. function:: getrecursionlimit() |
| 424 | |
| 425 | Return the current value of the recursion limit, the maximum depth of the Python |
| 426 | interpreter stack. This limit prevents infinite recursion from causing an |
| 427 | overflow of the C stack and crashing Python. It can be set by |
| 428 | :func:`setrecursionlimit`. |
| 429 | |
| 430 | |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 431 | .. function:: getsizeof(object[, default]) |
Martin v. Löwis | 00709aa | 2008-06-04 14:18:43 +0000 | [diff] [blame] | 432 | |
| 433 | Return the size of an object in bytes. The object can be any type of |
| 434 | object. All built-in objects will return correct results, but this |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 435 | does not have to hold true for third-party extensions as it is implementation |
Martin v. Löwis | 00709aa | 2008-06-04 14:18:43 +0000 | [diff] [blame] | 436 | specific. |
| 437 | |
Benjamin Peterson | 4ac9ce4 | 2009-10-04 14:49:41 +0000 | [diff] [blame] | 438 | If given, *default* will be returned if the object does not provide means to |
Georg Brandl | ef871f6 | 2010-03-12 10:06:40 +0000 | [diff] [blame] | 439 | retrieve the size. Otherwise a :exc:`TypeError` will be raised. |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 440 | |
Benjamin Peterson | 4ac9ce4 | 2009-10-04 14:49:41 +0000 | [diff] [blame] | 441 | :func:`getsizeof` calls the object's ``__sizeof__`` method and adds an |
| 442 | additional garbage collector overhead if the object is managed by the garbage |
| 443 | collector. |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 444 | |
Raymond Hettinger | c539a2a | 2010-12-17 23:31:30 +0000 | [diff] [blame] | 445 | See `recursive sizeof recipe <http://code.activestate.com/recipes/577504>`_ |
| 446 | for an example of using :func:`getsizeof` recursively to find the size of |
| 447 | containers and all their contents. |
Martin v. Löwis | 00709aa | 2008-06-04 14:18:43 +0000 | [diff] [blame] | 448 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 449 | .. function:: getswitchinterval() |
| 450 | |
| 451 | Return the interpreter's "thread switch interval"; see |
| 452 | :func:`setswitchinterval`. |
| 453 | |
Antoine Pitrou | 79707ca | 2009-11-11 22:03:32 +0000 | [diff] [blame] | 454 | .. versionadded:: 3.2 |
| 455 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 456 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 457 | .. function:: _getframe([depth]) |
| 458 | |
| 459 | Return a frame object from the call stack. If optional integer *depth* is |
| 460 | given, return the frame object that many calls below the top of the stack. If |
| 461 | that is deeper than the call stack, :exc:`ValueError` is raised. The default |
| 462 | for *depth* is zero, returning the frame at the top of the call stack. |
| 463 | |
Georg Brandl | 495f7b5 | 2009-10-27 15:28:25 +0000 | [diff] [blame] | 464 | .. impl-detail:: |
| 465 | |
| 466 | This function should be used for internal and specialized purposes only. |
| 467 | It is not guaranteed to exist in all implementations of Python. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 468 | |
| 469 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 470 | .. function:: getprofile() |
| 471 | |
| 472 | .. index:: |
| 473 | single: profile function |
| 474 | single: profiler |
| 475 | |
| 476 | Get the profiler function as set by :func:`setprofile`. |
| 477 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 478 | |
| 479 | .. function:: gettrace() |
| 480 | |
| 481 | .. index:: |
| 482 | single: trace function |
| 483 | single: debugger |
| 484 | |
| 485 | Get the trace function as set by :func:`settrace`. |
| 486 | |
Georg Brandl | 495f7b5 | 2009-10-27 15:28:25 +0000 | [diff] [blame] | 487 | .. impl-detail:: |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 488 | |
| 489 | The :func:`gettrace` function is intended only for implementing debuggers, |
Georg Brandl | 495f7b5 | 2009-10-27 15:28:25 +0000 | [diff] [blame] | 490 | profilers, coverage tools and the like. Its behavior is part of the |
| 491 | implementation platform, rather than part of the language definition, and |
| 492 | thus may not be available in all Python implementations. |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 493 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 494 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 495 | .. function:: getwindowsversion() |
| 496 | |
Eric Smith | 7338a39 | 2010-01-27 00:56:30 +0000 | [diff] [blame] | 497 | Return a named tuple describing the Windows version |
Eric Smith | f7bb578 | 2010-01-27 00:44:57 +0000 | [diff] [blame] | 498 | currently running. The named elements are *major*, *minor*, |
| 499 | *build*, *platform*, *service_pack*, *service_pack_minor*, |
| 500 | *service_pack_major*, *suite_mask*, and *product_type*. |
| 501 | *service_pack* contains a string while all other values are |
| 502 | integers. The components can also be accessed by name, so |
| 503 | ``sys.getwindowsversion()[0]`` is equivalent to |
| 504 | ``sys.getwindowsversion().major``. For compatibility with prior |
| 505 | versions, only the first 5 elements are retrievable by indexing. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 506 | |
| 507 | *platform* may be one of the following values: |
| 508 | |
Christian Heimes | 81ee3ef | 2008-05-04 22:42:01 +0000 | [diff] [blame] | 509 | +-----------------------------------------+-------------------------+ |
| 510 | | Constant | Platform | |
| 511 | +=========================================+=========================+ |
| 512 | | :const:`0 (VER_PLATFORM_WIN32s)` | Win32s on Windows 3.1 | |
| 513 | +-----------------------------------------+-------------------------+ |
| 514 | | :const:`1 (VER_PLATFORM_WIN32_WINDOWS)` | Windows 95/98/ME | |
| 515 | +-----------------------------------------+-------------------------+ |
| 516 | | :const:`2 (VER_PLATFORM_WIN32_NT)` | Windows NT/2000/XP/x64 | |
| 517 | +-----------------------------------------+-------------------------+ |
| 518 | | :const:`3 (VER_PLATFORM_WIN32_CE)` | Windows CE | |
| 519 | +-----------------------------------------+-------------------------+ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 520 | |
Eric Smith | f7bb578 | 2010-01-27 00:44:57 +0000 | [diff] [blame] | 521 | *product_type* may be one of the following values: |
| 522 | |
| 523 | +---------------------------------------+---------------------------------+ |
| 524 | | Constant | Meaning | |
| 525 | +=======================================+=================================+ |
| 526 | | :const:`1 (VER_NT_WORKSTATION)` | The system is a workstation. | |
| 527 | +---------------------------------------+---------------------------------+ |
| 528 | | :const:`2 (VER_NT_DOMAIN_CONTROLLER)` | The system is a domain | |
| 529 | | | controller. | |
| 530 | +---------------------------------------+---------------------------------+ |
| 531 | | :const:`3 (VER_NT_SERVER)` | The system is a server, but not | |
| 532 | | | a domain controller. | |
| 533 | +---------------------------------------+---------------------------------+ |
| 534 | |
| 535 | |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 536 | This function wraps the Win32 :c:func:`GetVersionEx` function; see the |
| 537 | Microsoft documentation on :c:func:`OSVERSIONINFOEX` for more information |
Eric Smith | f7bb578 | 2010-01-27 00:44:57 +0000 | [diff] [blame] | 538 | about these fields. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 539 | |
| 540 | Availability: Windows. |
| 541 | |
Ezio Melotti | 83fc6dd | 2010-01-27 22:44:03 +0000 | [diff] [blame] | 542 | .. versionchanged:: 3.2 |
Eric Smith | f7bb578 | 2010-01-27 00:44:57 +0000 | [diff] [blame] | 543 | Changed to a named tuple and added *service_pack_minor*, |
| 544 | *service_pack_major*, *suite_mask*, and *product_type*. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 545 | |
Mark Dickinson | dc787d2 | 2010-05-23 13:33:13 +0000 | [diff] [blame] | 546 | |
| 547 | .. data:: hash_info |
| 548 | |
Benjamin Peterson | 2b8ef2d | 2011-04-20 18:31:22 -0500 | [diff] [blame] | 549 | A :term:`struct sequence` giving parameters of the numeric hash |
| 550 | implementation. For more details about hashing of numeric types, see |
| 551 | :ref:`numeric-hash`. |
Mark Dickinson | dc787d2 | 2010-05-23 13:33:13 +0000 | [diff] [blame] | 552 | |
| 553 | +---------------------+--------------------------------------------------+ |
| 554 | | attribute | explanation | |
| 555 | +=====================+==================================================+ |
| 556 | | :const:`width` | width in bits used for hash values | |
| 557 | +---------------------+--------------------------------------------------+ |
| 558 | | :const:`modulus` | prime modulus P used for numeric hash scheme | |
| 559 | +---------------------+--------------------------------------------------+ |
| 560 | | :const:`inf` | hash value returned for a positive infinity | |
| 561 | +---------------------+--------------------------------------------------+ |
| 562 | | :const:`nan` | hash value returned for a nan | |
| 563 | +---------------------+--------------------------------------------------+ |
| 564 | | :const:`imag` | multiplier used for the imaginary part of a | |
| 565 | | | complex number | |
| 566 | +---------------------+--------------------------------------------------+ |
| 567 | |
| 568 | .. versionadded:: 3.2 |
| 569 | |
| 570 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 571 | .. data:: hexversion |
| 572 | |
| 573 | The version number encoded as a single integer. This is guaranteed to increase |
| 574 | with each version, including proper support for non-production releases. For |
| 575 | example, to test that the Python interpreter is at least version 1.5.2, use:: |
| 576 | |
| 577 | if sys.hexversion >= 0x010502F0: |
| 578 | # use some advanced feature |
| 579 | ... |
| 580 | else: |
| 581 | # use an alternative implementation or warn the user |
| 582 | ... |
| 583 | |
| 584 | This is called ``hexversion`` since it only really looks meaningful when viewed |
| 585 | as the result of passing it to the built-in :func:`hex` function. The |
Éric Araujo | 0abb8b7 | 2011-04-27 16:32:36 +0200 | [diff] [blame] | 586 | :term:`struct sequence` :data:`sys.version_info` may be used for a more |
| 587 | human-friendly encoding of the same information. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 588 | |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 589 | The ``hexversion`` is a 32-bit number with the following layout: |
R David Murray | 2043f9c | 2011-04-25 16:12:26 -0400 | [diff] [blame] | 590 | |
| 591 | +-------------------------+------------------------------------------------+ |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 592 | | Bits (big endian order) | Meaning | |
R David Murray | 2043f9c | 2011-04-25 16:12:26 -0400 | [diff] [blame] | 593 | +=========================+================================================+ |
| 594 | | :const:`1-8` | ``PY_MAJOR_VERSION`` (the ``2`` in | |
| 595 | | | ``2.1.0a3``) | |
| 596 | +-------------------------+------------------------------------------------+ |
| 597 | | :const:`9-16` | ``PY_MINOR_VERSION`` (the ``1`` in | |
| 598 | | | ``2.1.0a3``) | |
| 599 | +-------------------------+------------------------------------------------+ |
| 600 | | :const:`17-24` | ``PY_MICRO_VERSION`` (the ``0`` in | |
| 601 | | | ``2.1.0a3``) | |
| 602 | +-------------------------+------------------------------------------------+ |
| 603 | | :const:`25-28` | ``PY_RELEASE_LEVEL`` (``0xA`` for alpha, | |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 604 | | | ``0xB`` for beta, ``0xC`` for release | |
| 605 | | | candidate and ``0xF`` for final) | |
R David Murray | 2043f9c | 2011-04-25 16:12:26 -0400 | [diff] [blame] | 606 | +-------------------------+------------------------------------------------+ |
| 607 | | :const:`29-32` | ``PY_RELEASE_SERIAL`` (the ``3`` in | |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 608 | | | ``2.1.0a3``, zero for final releases) | |
R David Murray | 2043f9c | 2011-04-25 16:12:26 -0400 | [diff] [blame] | 609 | +-------------------------+------------------------------------------------+ |
| 610 | |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 611 | Thus ``2.1.0a3`` is hexversion ``0x020100a3``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 612 | |
Mark Dickinson | bd79264 | 2009-03-18 20:06:12 +0000 | [diff] [blame] | 613 | .. data:: int_info |
| 614 | |
Benjamin Peterson | 2b8ef2d | 2011-04-20 18:31:22 -0500 | [diff] [blame] | 615 | A :term:`struct sequence` that holds information about Python's internal |
| 616 | representation of integers. The attributes are read only. |
Mark Dickinson | bd79264 | 2009-03-18 20:06:12 +0000 | [diff] [blame] | 617 | |
| 618 | +-------------------------+----------------------------------------------+ |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 619 | | Attribute | Explanation | |
Mark Dickinson | bd79264 | 2009-03-18 20:06:12 +0000 | [diff] [blame] | 620 | +=========================+==============================================+ |
| 621 | | :const:`bits_per_digit` | number of bits held in each digit. Python | |
| 622 | | | integers are stored internally in base | |
| 623 | | | ``2**int_info.bits_per_digit`` | |
| 624 | +-------------------------+----------------------------------------------+ |
| 625 | | :const:`sizeof_digit` | size in bytes of the C type used to | |
| 626 | | | represent a digit | |
| 627 | +-------------------------+----------------------------------------------+ |
| 628 | |
Mark Dickinson | d72c7b6 | 2009-03-20 16:00:49 +0000 | [diff] [blame] | 629 | .. versionadded:: 3.1 |
| 630 | |
Mark Dickinson | bd79264 | 2009-03-18 20:06:12 +0000 | [diff] [blame] | 631 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 632 | .. function:: intern(string) |
| 633 | |
| 634 | Enter *string* in the table of "interned" strings and return the interned string |
| 635 | -- which is *string* itself or a copy. Interning strings is useful to gain a |
| 636 | little performance on dictionary lookup -- if the keys in a dictionary are |
| 637 | interned, and the lookup key is interned, the key comparisons (after hashing) |
| 638 | can be done by a pointer compare instead of a string compare. Normally, the |
| 639 | names used in Python programs are automatically interned, and the dictionaries |
| 640 | used to hold module, class or instance attributes have interned keys. |
| 641 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 642 | Interned strings are not immortal; you must keep a reference to the return |
| 643 | value of :func:`intern` around to benefit from it. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 644 | |
| 645 | |
| 646 | .. data:: last_type |
| 647 | last_value |
| 648 | last_traceback |
| 649 | |
| 650 | These three variables are not always defined; they are set when an exception is |
| 651 | not handled and the interpreter prints an error message and a stack traceback. |
| 652 | Their intended use is to allow an interactive user to import a debugger module |
| 653 | and engage in post-mortem debugging without having to re-execute the command |
| 654 | that caused the error. (Typical use is ``import pdb; pdb.pm()`` to enter the |
Alexander Belopolsky | f0a0d14 | 2010-10-27 03:06:43 +0000 | [diff] [blame] | 655 | post-mortem debugger; see :mod:`pdb` module for |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 656 | more information.) |
| 657 | |
| 658 | The meaning of the variables is the same as that of the return values from |
Georg Brandl | 482b151 | 2010-03-21 09:02:59 +0000 | [diff] [blame] | 659 | :func:`exc_info` above. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 660 | |
| 661 | |
Christian Heimes | a37d4c6 | 2007-12-04 23:02:19 +0000 | [diff] [blame] | 662 | .. data:: maxsize |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 663 | |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 664 | An integer giving the maximum value a variable of type :c:type:`Py_ssize_t` can |
Georg Brandl | 3377055 | 2007-12-15 09:55:35 +0000 | [diff] [blame] | 665 | take. It's usually ``2**31 - 1`` on a 32-bit platform and ``2**63 - 1`` on a |
| 666 | 64-bit platform. |
Christian Heimes | a37d4c6 | 2007-12-04 23:02:19 +0000 | [diff] [blame] | 667 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 668 | |
| 669 | .. data:: maxunicode |
| 670 | |
Ezio Melotti | 48a2f8f | 2011-09-29 00:18:19 +0300 | [diff] [blame] | 671 | An integer giving the value of the largest Unicode code point, |
| 672 | i.e. ``1114111`` (``0x10FFFF`` in hexadecimal). |
| 673 | |
| 674 | .. versionchanged:: 3.3 |
Éric Araujo | 525b1e9 | 2011-10-05 01:06:31 +0200 | [diff] [blame] | 675 | Before :pep:`393`, ``sys.maxunicode`` used to be either ``0xFFFF`` |
Ezio Melotti | 48a2f8f | 2011-09-29 00:18:19 +0300 | [diff] [blame] | 676 | or ``0x10FFFF``, depending on the configuration option that specified |
| 677 | whether Unicode characters were stored as UCS-2 or UCS-4. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 678 | |
| 679 | |
Brett Cannon | e43b060 | 2009-03-21 03:11:16 +0000 | [diff] [blame] | 680 | .. data:: meta_path |
| 681 | |
| 682 | A list of :term:`finder` objects that have their :meth:`find_module` |
| 683 | methods called to see if one of the objects can find the module to be |
| 684 | imported. The :meth:`find_module` method is called at least with the |
| 685 | absolute name of the module being imported. If the module to be imported is |
| 686 | contained in package then the parent package's :attr:`__path__` attribute |
Georg Brandl | 375aec2 | 2011-01-15 17:03:02 +0000 | [diff] [blame] | 687 | is passed in as a second argument. The method returns ``None`` if |
Brett Cannon | e43b060 | 2009-03-21 03:11:16 +0000 | [diff] [blame] | 688 | the module cannot be found, else returns a :term:`loader`. |
| 689 | |
| 690 | :data:`sys.meta_path` is searched before any implicit default finders or |
| 691 | :data:`sys.path`. |
| 692 | |
| 693 | See :pep:`302` for the original specification. |
| 694 | |
| 695 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 696 | .. data:: modules |
| 697 | |
| 698 | This is a dictionary that maps module names to modules which have already been |
| 699 | loaded. This can be manipulated to force reloading of modules and other tricks. |
| 700 | |
| 701 | |
| 702 | .. data:: path |
| 703 | |
| 704 | .. index:: triple: module; search; path |
| 705 | |
| 706 | A list of strings that specifies the search path for modules. Initialized from |
| 707 | the environment variable :envvar:`PYTHONPATH`, plus an installation-dependent |
| 708 | default. |
| 709 | |
| 710 | As initialized upon program startup, the first item of this list, ``path[0]``, |
| 711 | is the directory containing the script that was used to invoke the Python |
| 712 | interpreter. If the script directory is not available (e.g. if the interpreter |
| 713 | is invoked interactively or if the script is read from standard input), |
| 714 | ``path[0]`` is the empty string, which directs Python to search modules in the |
| 715 | current directory first. Notice that the script directory is inserted *before* |
| 716 | the entries inserted as a result of :envvar:`PYTHONPATH`. |
| 717 | |
| 718 | A program is free to modify this list for its own purposes. |
| 719 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 720 | |
Benjamin Peterson | 058e31e | 2009-01-16 03:54:08 +0000 | [diff] [blame] | 721 | .. seealso:: |
| 722 | Module :mod:`site` This describes how to use .pth files to extend |
| 723 | :data:`sys.path`. |
| 724 | |
| 725 | |
Brett Cannon | e43b060 | 2009-03-21 03:11:16 +0000 | [diff] [blame] | 726 | .. data:: path_hooks |
| 727 | |
| 728 | A list of callables that take a path argument to try to create a |
| 729 | :term:`finder` for the path. If a finder can be created, it is to be |
| 730 | returned by the callable, else raise :exc:`ImportError`. |
| 731 | |
| 732 | Originally specified in :pep:`302`. |
| 733 | |
| 734 | |
| 735 | .. data:: path_importer_cache |
| 736 | |
| 737 | A dictionary acting as a cache for :term:`finder` objects. The keys are |
| 738 | paths that have been passed to :data:`sys.path_hooks` and the values are |
| 739 | the finders that are found. If a path is a valid file system path but no |
Georg Brandl | 375aec2 | 2011-01-15 17:03:02 +0000 | [diff] [blame] | 740 | explicit finder is found on :data:`sys.path_hooks` then ``None`` is |
Brett Cannon | e43b060 | 2009-03-21 03:11:16 +0000 | [diff] [blame] | 741 | stored to represent the implicit default finder should be used. If the path |
| 742 | is not an existing path then :class:`imp.NullImporter` is set. |
| 743 | |
| 744 | Originally specified in :pep:`302`. |
| 745 | |
| 746 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 747 | .. data:: platform |
| 748 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 749 | This string contains a platform identifier that can be used to append |
| 750 | platform-specific components to :data:`sys.path`, for instance. |
| 751 | |
Victor Stinner | 795eaeb | 2011-08-21 12:08:11 +0200 | [diff] [blame] | 752 | For Unix systems, except on Linux, this is the lowercased OS name as |
| 753 | returned by ``uname -s`` with the first part of the version as returned by |
| 754 | ``uname -r`` appended, e.g. ``'sunos5'`` or ``'freebsd8'``, *at the time |
| 755 | when Python was built*. Unless you want to test for a specific system |
| 756 | version, it is therefore recommended to use the following idiom:: |
Antoine Pitrou | a83cdaa | 2011-07-09 15:54:23 +0200 | [diff] [blame] | 757 | |
Victor Stinner | 795eaeb | 2011-08-21 12:08:11 +0200 | [diff] [blame] | 758 | if sys.platform.startswith('freebsd'): |
| 759 | # FreeBSD-specific code here... |
Georg Brandl | a47e53e | 2011-09-03 09:26:09 +0200 | [diff] [blame] | 760 | elif sys.platform.startswith('linux'): |
Antoine Pitrou | a83cdaa | 2011-07-09 15:54:23 +0200 | [diff] [blame] | 761 | # Linux-specific code here... |
| 762 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 763 | For other systems, the values are: |
| 764 | |
| 765 | ================ =========================== |
| 766 | System :data:`platform` value |
| 767 | ================ =========================== |
Victor Stinner | 795eaeb | 2011-08-21 12:08:11 +0200 | [diff] [blame] | 768 | Linux ``'linux'`` |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 769 | Windows ``'win32'`` |
| 770 | Windows/Cygwin ``'cygwin'`` |
Georg Brandl | c575c90 | 2008-09-13 17:46:05 +0000 | [diff] [blame] | 771 | Mac OS X ``'darwin'`` |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 772 | OS/2 ``'os2'`` |
| 773 | OS/2 EMX ``'os2emx'`` |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 774 | ================ =========================== |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 775 | |
Victor Stinner | 795eaeb | 2011-08-21 12:08:11 +0200 | [diff] [blame] | 776 | .. versionchanged:: 3.3 |
| 777 | On Linux, :attr:`sys.platform` doesn't contain the major version anymore. |
Georg Brandl | fbd1e04 | 2011-09-04 08:42:26 +0200 | [diff] [blame] | 778 | It is always ``'linux'``, instead of ``'linux2'`` or ``'linux3'``. Since |
| 779 | older Python versions include the version number, it is recommended to |
| 780 | always use the ``startswith`` idiom presented above. |
Victor Stinner | 795eaeb | 2011-08-21 12:08:11 +0200 | [diff] [blame] | 781 | |
Antoine Pitrou | a83cdaa | 2011-07-09 15:54:23 +0200 | [diff] [blame] | 782 | .. seealso:: |
Georg Brandl | eb25fb7 | 2012-02-23 21:12:39 +0100 | [diff] [blame] | 783 | |
Antoine Pitrou | a83cdaa | 2011-07-09 15:54:23 +0200 | [diff] [blame] | 784 | :attr:`os.name` has a coarser granularity. :func:`os.uname` gives |
| 785 | system-dependent version information. |
| 786 | |
| 787 | The :mod:`platform` module provides detailed checks for the |
| 788 | system's identity. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 789 | |
Georg Brandl | fbd1e04 | 2011-09-04 08:42:26 +0200 | [diff] [blame] | 790 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 791 | .. data:: prefix |
| 792 | |
| 793 | A string giving the site-specific directory prefix where the platform |
| 794 | independent Python files are installed; by default, this is the string |
Éric Araujo | 713d303 | 2010-11-18 16:38:46 +0000 | [diff] [blame] | 795 | ``'/usr/local'``. This can be set at build time with the ``--prefix`` |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 796 | argument to the :program:`configure` script. The main collection of Python |
Georg Brandl | a673eb8 | 2012-03-04 16:17:05 +0100 | [diff] [blame] | 797 | library modules is installed in the directory :file:`{prefix}/lib/python{X.Y}` |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 798 | while the platform independent header files (all except :file:`pyconfig.h`) are |
Georg Brandl | eb25fb7 | 2012-02-23 21:12:39 +0100 | [diff] [blame] | 799 | stored in :file:`{prefix}/include/python{X.Y}`, where *X.Y* is the version |
Éric Araujo | 58a9153 | 2011-10-05 01:28:24 +0200 | [diff] [blame] | 800 | number of Python, for example ``3.2``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 801 | |
Vinay Sajip | 7ded1f0 | 2012-05-26 03:45:29 +0100 | [diff] [blame^] | 802 | .. note:: If a virtual environment is in effect, this value will be changed |
| 803 | in ``site.py`` to point to the virtual environment. The value for the |
| 804 | Python installation will still be available, via :data:`base_prefix`. |
| 805 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 806 | |
| 807 | .. data:: ps1 |
| 808 | ps2 |
| 809 | |
| 810 | .. index:: |
| 811 | single: interpreter prompts |
| 812 | single: prompts, interpreter |
| 813 | |
| 814 | Strings specifying the primary and secondary prompt of the interpreter. These |
| 815 | are only defined if the interpreter is in interactive mode. Their initial |
| 816 | values in this case are ``'>>> '`` and ``'... '``. If a non-string object is |
| 817 | assigned to either variable, its :func:`str` is re-evaluated each time the |
| 818 | interpreter prepares to read a new interactive command; this can be used to |
| 819 | implement a dynamic prompt. |
| 820 | |
| 821 | |
| 822 | .. function:: setcheckinterval(interval) |
| 823 | |
| 824 | Set the interpreter's "check interval". This integer value determines how often |
| 825 | the interpreter checks for periodic things such as thread switches and signal |
| 826 | handlers. The default is ``100``, meaning the check is performed every 100 |
| 827 | Python virtual instructions. Setting it to a larger value may increase |
| 828 | performance for programs using threads. Setting it to a value ``<=`` 0 checks |
| 829 | every virtual instruction, maximizing responsiveness as well as overhead. |
| 830 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 831 | .. deprecated:: 3.2 |
Georg Brandl | 67b21b7 | 2010-08-17 15:07:14 +0000 | [diff] [blame] | 832 | This function doesn't have an effect anymore, as the internal logic for |
| 833 | thread switching and asynchronous tasks has been rewritten. Use |
| 834 | :func:`setswitchinterval` instead. |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 835 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 836 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 837 | .. function:: setdlopenflags(n) |
| 838 | |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 839 | Set the flags used by the interpreter for :c:func:`dlopen` calls, such as when |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 840 | the interpreter loads extension modules. Among other things, this will enable a |
| 841 | lazy resolving of symbols when importing a module, if called as |
| 842 | ``sys.setdlopenflags(0)``. To share symbols across extension modules, call as |
Victor Stinner | 8b905bd | 2011-10-25 13:34:04 +0200 | [diff] [blame] | 843 | ``sys.setdlopenflags(os.RTLD_GLOBAL)``. Symbolic names for the flag modules |
| 844 | can be found in the :mod:`os` module (``RTLD_xxx`` constants, e.g. |
| 845 | :data:`os.RTLD_LAZY`). |
| 846 | |
| 847 | Availability: Unix. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 848 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 849 | .. function:: setprofile(profilefunc) |
| 850 | |
| 851 | .. index:: |
| 852 | single: profile function |
| 853 | single: profiler |
| 854 | |
| 855 | Set the system's profile function, which allows you to implement a Python source |
| 856 | code profiler in Python. See chapter :ref:`profile` for more information on the |
| 857 | Python profiler. The system's profile function is called similarly to the |
| 858 | system's trace function (see :func:`settrace`), but it isn't called for each |
| 859 | executed line of code (only on call and return, but the return event is reported |
| 860 | even when an exception has been set). The function is thread-specific, but |
| 861 | there is no way for the profiler to know about context switches between threads, |
| 862 | so it does not make sense to use this in the presence of multiple threads. Also, |
| 863 | its return value is not used, so it can simply return ``None``. |
| 864 | |
| 865 | |
| 866 | .. function:: setrecursionlimit(limit) |
| 867 | |
| 868 | Set the maximum depth of the Python interpreter stack to *limit*. This limit |
| 869 | prevents infinite recursion from causing an overflow of the C stack and crashing |
| 870 | Python. |
| 871 | |
| 872 | The highest possible limit is platform-dependent. A user may need to set the |
Georg Brandl | 5166375 | 2011-05-13 06:55:28 +0200 | [diff] [blame] | 873 | limit higher when they have a program that requires deep recursion and a platform |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 874 | that supports a higher limit. This should be done with care, because a too-high |
| 875 | limit can lead to a crash. |
| 876 | |
| 877 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 878 | .. function:: setswitchinterval(interval) |
| 879 | |
| 880 | Set the interpreter's thread switch interval (in seconds). This floating-point |
| 881 | value determines the ideal duration of the "timeslices" allocated to |
| 882 | concurrently running Python threads. Please note that the actual value |
| 883 | can be higher, especially if long-running internal functions or methods |
| 884 | are used. Also, which thread becomes scheduled at the end of the interval |
| 885 | is the operating system's decision. The interpreter doesn't have its |
| 886 | own scheduler. |
| 887 | |
Antoine Pitrou | 79707ca | 2009-11-11 22:03:32 +0000 | [diff] [blame] | 888 | .. versionadded:: 3.2 |
| 889 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 890 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 891 | .. function:: settrace(tracefunc) |
| 892 | |
| 893 | .. index:: |
| 894 | single: trace function |
| 895 | single: debugger |
| 896 | |
| 897 | Set the system's trace function, which allows you to implement a Python |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 898 | source code debugger in Python. The function is thread-specific; for a |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 899 | debugger to support multiple threads, it must be registered using |
| 900 | :func:`settrace` for each thread being debugged. |
| 901 | |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 902 | Trace functions should have three arguments: *frame*, *event*, and |
| 903 | *arg*. *frame* is the current stack frame. *event* is a string: ``'call'``, |
| 904 | ``'line'``, ``'return'``, ``'exception'``, ``'c_call'``, ``'c_return'``, or |
| 905 | ``'c_exception'``. *arg* depends on the event type. |
| 906 | |
| 907 | The trace function is invoked (with *event* set to ``'call'``) whenever a new |
| 908 | local scope is entered; it should return a reference to a local trace |
| 909 | function to be used that scope, or ``None`` if the scope shouldn't be traced. |
| 910 | |
| 911 | The local trace function should return a reference to itself (or to another |
| 912 | function for further tracing in that scope), or ``None`` to turn off tracing |
| 913 | in that scope. |
| 914 | |
| 915 | The events have the following meaning: |
| 916 | |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 917 | ``'call'`` |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 918 | A function is called (or some other code block entered). The |
| 919 | global trace function is called; *arg* is ``None``; the return value |
| 920 | specifies the local trace function. |
| 921 | |
| 922 | ``'line'`` |
Alexandre Vassalotti | 7b82b40 | 2009-07-21 04:30:03 +0000 | [diff] [blame] | 923 | The interpreter is about to execute a new line of code or re-execute the |
| 924 | condition of a loop. The local trace function is called; *arg* is |
| 925 | ``None``; the return value specifies the new local trace function. See |
| 926 | :file:`Objects/lnotab_notes.txt` for a detailed explanation of how this |
| 927 | works. |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 928 | |
| 929 | ``'return'`` |
| 930 | A function (or other code block) is about to return. The local trace |
Georg Brandl | d0b0e1d | 2010-10-15 16:42:37 +0000 | [diff] [blame] | 931 | function is called; *arg* is the value that will be returned, or ``None`` |
| 932 | if the event is caused by an exception being raised. The trace function's |
| 933 | return value is ignored. |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 934 | |
| 935 | ``'exception'`` |
| 936 | An exception has occurred. The local trace function is called; *arg* is a |
| 937 | tuple ``(exception, value, traceback)``; the return value specifies the |
| 938 | new local trace function. |
| 939 | |
| 940 | ``'c_call'`` |
| 941 | A C function is about to be called. This may be an extension function or |
Georg Brandl | 22b3431 | 2009-07-26 14:54:51 +0000 | [diff] [blame] | 942 | a built-in. *arg* is the C function object. |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 943 | |
| 944 | ``'c_return'`` |
Georg Brandl | d0b0e1d | 2010-10-15 16:42:37 +0000 | [diff] [blame] | 945 | A C function has returned. *arg* is the C function object. |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 946 | |
| 947 | ``'c_exception'`` |
Georg Brandl | d0b0e1d | 2010-10-15 16:42:37 +0000 | [diff] [blame] | 948 | A C function has raised an exception. *arg* is the C function object. |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 949 | |
| 950 | Note that as an exception is propagated down the chain of callers, an |
| 951 | ``'exception'`` event is generated at each level. |
| 952 | |
| 953 | For more information on code and frame objects, refer to :ref:`types`. |
| 954 | |
Georg Brandl | 495f7b5 | 2009-10-27 15:28:25 +0000 | [diff] [blame] | 955 | .. impl-detail:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 956 | |
| 957 | The :func:`settrace` function is intended only for implementing debuggers, |
Georg Brandl | 495f7b5 | 2009-10-27 15:28:25 +0000 | [diff] [blame] | 958 | profilers, coverage tools and the like. Its behavior is part of the |
| 959 | implementation platform, rather than part of the language definition, and |
| 960 | thus may not be available in all Python implementations. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 961 | |
| 962 | |
| 963 | .. function:: settscdump(on_flag) |
| 964 | |
| 965 | Activate dumping of VM measurements using the Pentium timestamp counter, if |
| 966 | *on_flag* is true. Deactivate these dumps if *on_flag* is off. The function is |
Éric Araujo | 713d303 | 2010-11-18 16:38:46 +0000 | [diff] [blame] | 967 | available only if Python was compiled with ``--with-tsc``. To understand |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 968 | the output of this dump, read :file:`Python/ceval.c` in the Python sources. |
| 969 | |
Benjamin Peterson | 21896a3 | 2010-03-21 22:03:03 +0000 | [diff] [blame] | 970 | .. impl-detail:: |
| 971 | This function is intimately bound to CPython implementation details and |
| 972 | thus not likely to be implemented elsewhere. |
| 973 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 974 | |
| 975 | .. data:: stdin |
| 976 | stdout |
| 977 | stderr |
| 978 | |
Antoine Pitrou | 7158e06 | 2011-12-15 16:25:34 +0100 | [diff] [blame] | 979 | :term:`File objects <file object>` used by the interpreter for standard |
| 980 | input, output and errors: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 981 | |
Antoine Pitrou | 7158e06 | 2011-12-15 16:25:34 +0100 | [diff] [blame] | 982 | * ``stdin`` is used for all interactive input (including calls to |
| 983 | :func:`input`); |
| 984 | * ``stdout`` is used for the output of :func:`print` and :term:`expression` |
| 985 | statements and for the prompts of :func:`input`; |
| 986 | * The interpreter's own prompts and its error messages go to ``stderr``. |
| 987 | |
| 988 | By default, these streams are regular text streams as returned by the |
| 989 | :func:`open` function. Their parameters are chosen as follows: |
| 990 | |
| 991 | * The character encoding is platform-dependent. Under Windows, if the stream |
| 992 | is interactive (that is, if its :meth:`isatty` method returns True), the |
| 993 | console codepage is used, otherwise the ANSI code page. Under other |
| 994 | platforms, the locale encoding is used (see :meth:`locale.getpreferredencoding`). |
| 995 | |
| 996 | Under all platforms though, you can override this value by setting the |
| 997 | :envvar:`PYTHONIOENCODING` environment variable. |
| 998 | |
| 999 | * When interactive, standard streams are line-buffered. Otherwise, they |
| 1000 | are block-buffered like regular text files. You can override this |
| 1001 | value with the :option:`-u` command-line option. |
| 1002 | |
| 1003 | To write or read binary data from/to the standard streams, use the |
| 1004 | underlying binary :data:`~io.TextIOBase.buffer`. For example, to write |
| 1005 | bytes to :data:`stdout`, use ``sys.stdout.buffer.write(b'abc')``. Using |
| 1006 | :meth:`io.TextIOBase.detach`, streams can be made binary by default. This |
Benjamin Peterson | 995bb47 | 2009-06-14 18:41:18 +0000 | [diff] [blame] | 1007 | function sets :data:`stdin` and :data:`stdout` to binary:: |
Benjamin Peterson | 4199d60 | 2009-05-12 20:47:57 +0000 | [diff] [blame] | 1008 | |
| 1009 | def make_streams_binary(): |
| 1010 | sys.stdin = sys.stdin.detach() |
Benjamin Peterson | 4487f53 | 2009-05-13 21:15:03 +0000 | [diff] [blame] | 1011 | sys.stdout = sys.stdout.detach() |
Benjamin Peterson | 995bb47 | 2009-06-14 18:41:18 +0000 | [diff] [blame] | 1012 | |
Antoine Pitrou | 7158e06 | 2011-12-15 16:25:34 +0100 | [diff] [blame] | 1013 | Note that the streams may be replaced with objects (like :class:`io.StringIO`) |
| 1014 | that do not support the :attr:`~io.BufferedIOBase.buffer` attribute or the |
Benjamin Peterson | 995bb47 | 2009-06-14 18:41:18 +0000 | [diff] [blame] | 1015 | :meth:`~io.BufferedIOBase.detach` method and can raise :exc:`AttributeError` |
| 1016 | or :exc:`io.UnsupportedOperation`. |
Benjamin Peterson | eb9fc52 | 2008-12-07 14:58:03 +0000 | [diff] [blame] | 1017 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1018 | |
| 1019 | .. data:: __stdin__ |
| 1020 | __stdout__ |
| 1021 | __stderr__ |
| 1022 | |
| 1023 | These objects contain the original values of ``stdin``, ``stderr`` and |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 1024 | ``stdout`` at the start of the program. They are used during finalization, |
| 1025 | and could be useful to print to the actual standard stream no matter if the |
| 1026 | ``sys.std*`` object has been redirected. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1027 | |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 1028 | It can also be used to restore the actual files to known working file objects |
| 1029 | in case they have been overwritten with a broken object. However, the |
| 1030 | preferred way to do this is to explicitly save the previous stream before |
| 1031 | replacing it, and restore the saved object. |
Christian Heimes | 58cb1b8 | 2007-11-13 02:19:40 +0000 | [diff] [blame] | 1032 | |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 1033 | .. note:: |
| 1034 | Under some conditions ``stdin``, ``stdout`` and ``stderr`` as well as the |
| 1035 | original values ``__stdin__``, ``__stdout__`` and ``__stderr__`` can be |
| 1036 | None. It is usually the case for Windows GUI apps that aren't connected |
| 1037 | to a console and Python apps started with :program:`pythonw`. |
Christian Heimes | 58cb1b8 | 2007-11-13 02:19:40 +0000 | [diff] [blame] | 1038 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1039 | |
Victor Stinner | d5c355c | 2011-04-30 14:53:09 +0200 | [diff] [blame] | 1040 | .. data:: thread_info |
| 1041 | |
| 1042 | A :term:`struct sequence` holding information about the thread |
| 1043 | implementation. |
| 1044 | |
| 1045 | +------------------+---------------------------------------------------------+ |
| 1046 | | Attribute | Explanation | |
| 1047 | +==================+=========================================================+ |
| 1048 | | :const:`name` | Name of the thread implementation: | |
| 1049 | | | | |
| 1050 | | | * ``'nt'``: Windows threads | |
| 1051 | | | * ``'os2'``: OS/2 threads | |
| 1052 | | | * ``'pthread'``: POSIX threads | |
| 1053 | | | * ``'solaris'``: Solaris threads | |
| 1054 | +------------------+---------------------------------------------------------+ |
| 1055 | | :const:`lock` | Name of the lock implementation: | |
| 1056 | | | | |
| 1057 | | | * ``'semaphore'``: a lock uses a semaphore | |
| 1058 | | | * ``'mutex+cond'``: a lock uses a mutex | |
| 1059 | | | and a condition variable | |
| 1060 | | | * ``None`` if this information is unknown | |
| 1061 | +------------------+---------------------------------------------------------+ |
| 1062 | | :const:`version` | Name and version of the thread library. It is a string, | |
| 1063 | | | or ``None`` if these informations are unknown. | |
| 1064 | +------------------+---------------------------------------------------------+ |
| 1065 | |
| 1066 | .. versionadded:: 3.3 |
| 1067 | |
| 1068 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1069 | .. data:: tracebacklimit |
| 1070 | |
| 1071 | When this variable is set to an integer value, it determines the maximum number |
| 1072 | of levels of traceback information printed when an unhandled exception occurs. |
| 1073 | The default is ``1000``. When set to ``0`` or less, all traceback information |
| 1074 | is suppressed and only the exception type and value are printed. |
| 1075 | |
| 1076 | |
| 1077 | .. data:: version |
| 1078 | |
| 1079 | A string containing the version number of the Python interpreter plus additional |
Georg Brandl | e42a59d | 2010-07-31 20:05:31 +0000 | [diff] [blame] | 1080 | information on the build number and compiler used. This string is displayed |
| 1081 | when the interactive interpreter is started. Do not extract version information |
| 1082 | out of it, rather, use :data:`version_info` and the functions provided by the |
| 1083 | :mod:`platform` module. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1084 | |
| 1085 | |
| 1086 | .. data:: api_version |
| 1087 | |
| 1088 | The C API version for this interpreter. Programmers may find this useful when |
| 1089 | debugging version conflicts between Python and extension modules. |
| 1090 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1091 | |
| 1092 | .. data:: version_info |
| 1093 | |
| 1094 | A tuple containing the five components of the version number: *major*, *minor*, |
| 1095 | *micro*, *releaselevel*, and *serial*. All values except *releaselevel* are |
| 1096 | integers; the release level is ``'alpha'``, ``'beta'``, ``'candidate'``, or |
| 1097 | ``'final'``. The ``version_info`` value corresponding to the Python version 2.0 |
Eric Smith | 0e5b562 | 2009-02-06 01:32:42 +0000 | [diff] [blame] | 1098 | is ``(2, 0, 0, 'final', 0)``. The components can also be accessed by name, |
| 1099 | so ``sys.version_info[0]`` is equivalent to ``sys.version_info.major`` |
| 1100 | and so on. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1101 | |
Raymond Hettinger | 35a8836 | 2009-04-09 00:08:24 +0000 | [diff] [blame] | 1102 | .. versionchanged:: 3.1 |
Georg Brandl | 67b21b7 | 2010-08-17 15:07:14 +0000 | [diff] [blame] | 1103 | Added named component attributes. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1104 | |
| 1105 | .. data:: warnoptions |
| 1106 | |
| 1107 | This is an implementation detail of the warnings framework; do not modify this |
| 1108 | value. Refer to the :mod:`warnings` module for more information on the warnings |
| 1109 | framework. |
| 1110 | |
| 1111 | |
| 1112 | .. data:: winver |
| 1113 | |
| 1114 | The version number used to form registry keys on Windows platforms. This is |
| 1115 | stored as string resource 1000 in the Python DLL. The value is normally the |
| 1116 | first three characters of :const:`version`. It is provided in the :mod:`sys` |
| 1117 | module for informational purposes; modifying this value has no effect on the |
| 1118 | registry keys used by Python. Availability: Windows. |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 1119 | |
Antoine Pitrou | 9583cac | 2010-10-21 13:42:28 +0000 | [diff] [blame] | 1120 | |
| 1121 | .. data:: _xoptions |
| 1122 | |
| 1123 | A dictionary of the various implementation-specific flags passed through |
| 1124 | the :option:`-X` command-line option. Option names are either mapped to |
| 1125 | their values, if given explicitly, or to :const:`True`. Example:: |
| 1126 | |
| 1127 | $ ./python -Xa=b -Xc |
| 1128 | Python 3.2a3+ (py3k, Oct 16 2010, 20:14:50) |
| 1129 | [GCC 4.4.3] on linux2 |
| 1130 | Type "help", "copyright", "credits" or "license" for more information. |
| 1131 | >>> import sys |
| 1132 | >>> sys._xoptions |
| 1133 | {'a': 'b', 'c': True} |
| 1134 | |
| 1135 | .. impl-detail:: |
| 1136 | |
| 1137 | This is a CPython-specific way of accessing options passed through |
| 1138 | :option:`-X`. Other implementations may export them through other |
| 1139 | means, or not at all. |
| 1140 | |
| 1141 | .. versionadded:: 3.2 |
| 1142 | |
| 1143 | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 1144 | .. rubric:: Citations |
| 1145 | |
| 1146 | .. [C99] ISO/IEC 9899:1999. "Programming languages -- C." A public draft of this standard is available at http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf . |
| 1147 | |