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 |
Vinay Sajip | cd9b746 | 2012-07-09 10:37:01 +0100 | [diff] [blame] | 35 | :data:`exec_prefix`. If not running in a |
| 36 | :ref:`virtual environment <venv-def>`, the values will stay the same; if |
| 37 | ``site.py`` finds that a virtual environment is in use, the values of |
| 38 | :data:`prefix` and :data:`exec_prefix` will be changed to point to the |
| 39 | virtual environment, whereas :data:`base_prefix` and |
Vinay Sajip | 7ded1f0 | 2012-05-26 03:45:29 +0100 | [diff] [blame] | 40 | :data:`base_exec_prefix` will remain pointing to the base Python |
| 41 | installation (the one which the virtual environment was created from). |
| 42 | |
Georg Brandl | 039b01d | 2012-05-26 09:11:22 +0200 | [diff] [blame] | 43 | .. versionadded:: 3.3 |
| 44 | |
| 45 | |
Vinay Sajip | 7ded1f0 | 2012-05-26 03:45:29 +0100 | [diff] [blame] | 46 | .. data:: base_prefix |
| 47 | |
| 48 | Set during Python startup, before ``site.py`` is run, to the same value as |
Vinay Sajip | cd9b746 | 2012-07-09 10:37:01 +0100 | [diff] [blame] | 49 | :data:`prefix`. If not running in a :ref:`virtual environment <venv-def>`, the values |
Vinay Sajip | 7ded1f0 | 2012-05-26 03:45:29 +0100 | [diff] [blame] | 50 | will stay the same; if ``site.py`` finds that a virtual environment is in |
| 51 | use, the values of :data:`prefix` and :data:`exec_prefix` will be changed to |
| 52 | point to the virtual environment, whereas :data:`base_prefix` and |
| 53 | :data:`base_exec_prefix` will remain pointing to the base Python |
| 54 | installation (the one which the virtual environment was created from). |
| 55 | |
Georg Brandl | 039b01d | 2012-05-26 09:11:22 +0200 | [diff] [blame] | 56 | .. versionadded:: 3.3 |
| 57 | |
| 58 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 59 | .. data:: byteorder |
| 60 | |
| 61 | An indicator of the native byte order. This will have the value ``'big'`` on |
| 62 | big-endian (most-significant byte first) platforms, and ``'little'`` on |
| 63 | little-endian (least-significant byte first) platforms. |
| 64 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 65 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 66 | .. data:: builtin_module_names |
| 67 | |
| 68 | A tuple of strings giving the names of all modules that are compiled into this |
| 69 | Python interpreter. (This information is not available in any other way --- |
| 70 | ``modules.keys()`` only lists the imported modules.) |
| 71 | |
| 72 | |
Georg Brandl | 8527126 | 2010-10-17 11:06:14 +0000 | [diff] [blame] | 73 | .. function:: call_tracing(func, args) |
| 74 | |
| 75 | Call ``func(*args)``, while tracing is enabled. The tracing state is saved, |
| 76 | and restored afterwards. This is intended to be called from a debugger from |
| 77 | a checkpoint, to recursively debug some other code. |
| 78 | |
| 79 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 80 | .. data:: copyright |
| 81 | |
| 82 | A string containing the copyright pertaining to the Python interpreter. |
| 83 | |
| 84 | |
Christian Heimes | 15ebc88 | 2008-02-04 18:48:49 +0000 | [diff] [blame] | 85 | .. function:: _clear_type_cache() |
| 86 | |
| 87 | Clear the internal type cache. The type cache is used to speed up attribute |
| 88 | and method lookups. Use the function *only* to drop unnecessary references |
| 89 | during reference leak debugging. |
| 90 | |
| 91 | This function should be used for internal and specialized purposes only. |
Christian Heimes | 2685563 | 2008-01-27 23:50:43 +0000 | [diff] [blame] | 92 | |
Christian Heimes | 2685563 | 2008-01-27 23:50:43 +0000 | [diff] [blame] | 93 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 94 | .. function:: _current_frames() |
| 95 | |
| 96 | Return a dictionary mapping each thread's identifier to the topmost stack frame |
| 97 | currently active in that thread at the time the function is called. Note that |
| 98 | functions in the :mod:`traceback` module can build the call stack given such a |
| 99 | frame. |
| 100 | |
| 101 | This is most useful for debugging deadlock: this function does not require the |
| 102 | deadlocked threads' cooperation, and such threads' call stacks are frozen for as |
| 103 | long as they remain deadlocked. The frame returned for a non-deadlocked thread |
| 104 | may bear no relationship to that thread's current activity by the time calling |
| 105 | code examines the frame. |
| 106 | |
| 107 | This function should be used for internal and specialized purposes only. |
| 108 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 109 | |
David Malcolm | 49526f4 | 2012-06-22 14:55:41 -0400 | [diff] [blame] | 110 | .. function:: _debugmallocstats() |
| 111 | |
| 112 | Print low-level information to stderr about the state of CPython's memory |
| 113 | allocator. |
| 114 | |
| 115 | If Python is configured --with-pydebug, it also performs some expensive |
| 116 | internal consistency checks. |
| 117 | |
| 118 | .. versionadded:: 3.3 |
| 119 | |
| 120 | .. impl-detail:: |
| 121 | |
| 122 | This function is specific to CPython. The exact output format is not |
| 123 | defined here, and may change. |
| 124 | |
| 125 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 126 | .. data:: dllhandle |
| 127 | |
| 128 | Integer specifying the handle of the Python DLL. Availability: Windows. |
| 129 | |
| 130 | |
| 131 | .. function:: displayhook(value) |
| 132 | |
Victor Stinner | 13d49ee | 2010-12-04 17:24:33 +0000 | [diff] [blame] | 133 | If *value* is not ``None``, this function prints ``repr(value)`` to |
| 134 | ``sys.stdout``, and saves *value* in ``builtins._``. If ``repr(value)`` is |
| 135 | not encodable to ``sys.stdout.encoding`` with ``sys.stdout.errors`` error |
| 136 | handler (which is probably ``'strict'``), encode it to |
| 137 | ``sys.stdout.encoding`` with ``'backslashreplace'`` error handler. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 138 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 139 | ``sys.displayhook`` is called on the result of evaluating an :term:`expression` |
| 140 | entered in an interactive Python session. The display of these values can be |
| 141 | customized by assigning another one-argument function to ``sys.displayhook``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 142 | |
Victor Stinner | 13d49ee | 2010-12-04 17:24:33 +0000 | [diff] [blame] | 143 | Pseudo-code:: |
| 144 | |
| 145 | def displayhook(value): |
| 146 | if value is None: |
| 147 | return |
| 148 | # Set '_' to None to avoid recursion |
| 149 | builtins._ = None |
| 150 | text = repr(value) |
| 151 | try: |
| 152 | sys.stdout.write(text) |
| 153 | except UnicodeEncodeError: |
| 154 | bytes = text.encode(sys.stdout.encoding, 'backslashreplace') |
| 155 | if hasattr(sys.stdout, 'buffer'): |
| 156 | sys.stdout.buffer.write(bytes) |
| 157 | else: |
| 158 | text = bytes.decode(sys.stdout.encoding, 'strict') |
| 159 | sys.stdout.write(text) |
| 160 | sys.stdout.write("\n") |
| 161 | builtins._ = value |
| 162 | |
| 163 | .. versionchanged:: 3.2 |
| 164 | Use ``'backslashreplace'`` error handler on :exc:`UnicodeEncodeError`. |
| 165 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 166 | |
Éric Araujo | da27263 | 2011-10-05 01:17:38 +0200 | [diff] [blame] | 167 | .. data:: dont_write_bytecode |
| 168 | |
| 169 | If this is true, Python won't try to write ``.pyc`` or ``.pyo`` files on the |
| 170 | import of source modules. This value is initially set to ``True`` or |
| 171 | ``False`` depending on the :option:`-B` command line option and the |
| 172 | :envvar:`PYTHONDONTWRITEBYTECODE` environment variable, but you can set it |
| 173 | yourself to control bytecode file generation. |
| 174 | |
| 175 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 176 | .. function:: excepthook(type, value, traceback) |
| 177 | |
| 178 | This function prints out a given traceback and exception to ``sys.stderr``. |
| 179 | |
| 180 | When an exception is raised and uncaught, the interpreter calls |
| 181 | ``sys.excepthook`` with three arguments, the exception class, exception |
| 182 | instance, and a traceback object. In an interactive session this happens just |
| 183 | before control is returned to the prompt; in a Python program this happens just |
| 184 | before the program exits. The handling of such top-level exceptions can be |
| 185 | customized by assigning another three-argument function to ``sys.excepthook``. |
| 186 | |
| 187 | |
| 188 | .. data:: __displayhook__ |
| 189 | __excepthook__ |
| 190 | |
| 191 | These objects contain the original values of ``displayhook`` and ``excepthook`` |
| 192 | at the start of the program. They are saved so that ``displayhook`` and |
| 193 | ``excepthook`` can be restored in case they happen to get replaced with broken |
| 194 | objects. |
| 195 | |
| 196 | |
| 197 | .. function:: exc_info() |
| 198 | |
| 199 | This function returns a tuple of three values that give information about the |
| 200 | exception that is currently being handled. The information returned is specific |
| 201 | both to the current thread and to the current stack frame. If the current stack |
| 202 | frame is not handling an exception, the information is taken from the calling |
| 203 | stack frame, or its caller, and so on until a stack frame is found that is |
| 204 | handling an exception. Here, "handling an exception" is defined as "executing |
Benjamin Peterson | eec3d71 | 2008-06-11 15:59:43 +0000 | [diff] [blame] | 205 | an except clause." For any stack frame, only information about the exception |
| 206 | being currently handled is accessible. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 207 | |
| 208 | .. index:: object: traceback |
| 209 | |
Georg Brandl | 482b151 | 2010-03-21 09:02:59 +0000 | [diff] [blame] | 210 | If no exception is being handled anywhere on the stack, a tuple containing |
| 211 | three ``None`` values is returned. Otherwise, the values returned are |
| 212 | ``(type, value, traceback)``. Their meaning is: *type* gets the type of the |
| 213 | exception being handled (a subclass of :exc:`BaseException`); *value* gets |
| 214 | the exception instance (an instance of the exception type); *traceback* gets |
| 215 | a traceback object (see the Reference Manual) which encapsulates the call |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 216 | stack at the point where the exception originally occurred. |
| 217 | |
| 218 | .. warning:: |
| 219 | |
Georg Brandl | e6bcc91 | 2008-05-12 18:05:20 +0000 | [diff] [blame] | 220 | Assigning the *traceback* return value to a local variable in a function |
| 221 | that is handling an exception will cause a circular reference. Since most |
| 222 | functions don't need access to the traceback, the best solution is to use |
| 223 | something like ``exctype, value = sys.exc_info()[:2]`` to extract only the |
| 224 | exception type and value. If you do need the traceback, make sure to |
| 225 | delete it after use (best done with a :keyword:`try` |
| 226 | ... :keyword:`finally` statement) or to call :func:`exc_info` in a |
| 227 | function that does not itself handle an exception. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 228 | |
Georg Brandl | e6bcc91 | 2008-05-12 18:05:20 +0000 | [diff] [blame] | 229 | Such cycles are normally automatically reclaimed when garbage collection |
| 230 | is enabled and they become unreachable, but it remains more efficient to |
| 231 | avoid creating cycles. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 232 | |
| 233 | |
| 234 | .. data:: exec_prefix |
| 235 | |
| 236 | A string giving the site-specific directory prefix where the platform-dependent |
| 237 | 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] | 238 | be set at build time with the ``--exec-prefix`` argument to the |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 239 | :program:`configure` script. Specifically, all configuration files (e.g. the |
Éric Araujo | 58a9153 | 2011-10-05 01:28:24 +0200 | [diff] [blame] | 240 | :file:`pyconfig.h` header file) are installed in the directory |
Georg Brandl | eb25fb7 | 2012-02-23 21:12:39 +0100 | [diff] [blame] | 241 | :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] | 242 | installed in :file:`{exec_prefix}/lib/python{X.Y}/lib-dynload`, where *X.Y* |
| 243 | is the version number of Python, for example ``3.2``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 244 | |
Vinay Sajip | cd9b746 | 2012-07-09 10:37:01 +0100 | [diff] [blame] | 245 | .. note:: If a :ref:`virtual environment <venv-def>` is in effect, this |
| 246 | value will be changed in ``site.py`` to point to the virtual environment. |
| 247 | The value for the Python installation will still be available, via |
| 248 | :data:`base_exec_prefix`. |
Vinay Sajip | 7ded1f0 | 2012-05-26 03:45:29 +0100 | [diff] [blame] | 249 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 250 | |
| 251 | .. data:: executable |
| 252 | |
Petri Lehtinen | 9713321 | 2012-02-02 20:59:48 +0200 | [diff] [blame] | 253 | A string giving the absolute path of the executable binary for the Python |
| 254 | interpreter, on systems where this makes sense. If Python is unable to retrieve |
| 255 | the real path to its executable, :data:`sys.executable` will be an empty string |
| 256 | or ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 257 | |
| 258 | |
| 259 | .. function:: exit([arg]) |
| 260 | |
| 261 | Exit from Python. This is implemented by raising the :exc:`SystemExit` |
| 262 | exception, so cleanup actions specified by finally clauses of :keyword:`try` |
Georg Brandl | 6f4e68d | 2010-10-17 10:51:45 +0000 | [diff] [blame] | 263 | statements are honored, and it is possible to intercept the exit attempt at |
| 264 | an outer level. |
| 265 | |
| 266 | The optional argument *arg* can be an integer giving the exit status |
| 267 | (defaulting to zero), or another type of object. If it is an integer, zero |
| 268 | is considered "successful termination" and any nonzero value is considered |
| 269 | "abnormal termination" by shells and the like. Most systems require it to be |
| 270 | in the range 0-127, and produce undefined results otherwise. Some systems |
| 271 | have a convention for assigning specific meanings to specific exit codes, but |
| 272 | these are generally underdeveloped; Unix programs generally use 2 for command |
| 273 | line syntax errors and 1 for all other kind of errors. If another type of |
| 274 | object is passed, ``None`` is equivalent to passing zero, and any other |
| 275 | object is printed to :data:`stderr` and results in an exit code of 1. In |
| 276 | particular, ``sys.exit("some error message")`` is a quick way to exit a |
| 277 | program when an error occurs. |
| 278 | |
| 279 | Since :func:`exit` ultimately "only" raises an exception, it will only exit |
| 280 | the process when called from the main thread, and the exception is not |
| 281 | intercepted. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 282 | |
| 283 | |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 284 | .. data:: flags |
| 285 | |
Benjamin Peterson | 2b8ef2d | 2011-04-20 18:31:22 -0500 | [diff] [blame] | 286 | The :term:`struct sequence` *flags* exposes the status of command line |
| 287 | flags. The attributes are read only. |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 288 | |
Éric Araujo | 5ab4776 | 2011-03-26 00:47:04 +0100 | [diff] [blame] | 289 | ============================= ============================= |
| 290 | attribute flag |
| 291 | ============================= ============================= |
| 292 | :const:`debug` :option:`-d` |
Éric Araujo | 5ab4776 | 2011-03-26 00:47:04 +0100 | [diff] [blame] | 293 | :const:`inspect` :option:`-i` |
| 294 | :const:`interactive` :option:`-i` |
| 295 | :const:`optimize` :option:`-O` or :option:`-OO` |
| 296 | :const:`dont_write_bytecode` :option:`-B` |
| 297 | :const:`no_user_site` :option:`-s` |
| 298 | :const:`no_site` :option:`-S` |
| 299 | :const:`ignore_environment` :option:`-E` |
| 300 | :const:`verbose` :option:`-v` |
| 301 | :const:`bytes_warning` :option:`-b` |
Éric Araujo | 722bec4 | 2011-03-26 01:59:47 +0100 | [diff] [blame] | 302 | :const:`quiet` :option:`-q` |
Georg Brandl | 2daf6ae | 2012-02-20 19:54:16 +0100 | [diff] [blame] | 303 | :const:`hash_randomization` :option:`-R` |
Éric Araujo | 5ab4776 | 2011-03-26 00:47:04 +0100 | [diff] [blame] | 304 | ============================= ============================= |
Georg Brandl | 8aa7e99 | 2010-12-28 18:30:18 +0000 | [diff] [blame] | 305 | |
| 306 | .. versionchanged:: 3.2 |
| 307 | Added ``quiet`` attribute for the new :option:`-q` flag. |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 308 | |
Georg Brandl | 09a7c72 | 2012-02-20 21:31:46 +0100 | [diff] [blame] | 309 | .. versionadded:: 3.2.3 |
Georg Brandl | 2daf6ae | 2012-02-20 19:54:16 +0100 | [diff] [blame] | 310 | The ``hash_randomization`` attribute. |
| 311 | |
Éric Araujo | 3e89870 | 2011-04-24 04:37:00 +0200 | [diff] [blame] | 312 | .. versionchanged:: 3.3 |
| 313 | Removed obsolete ``division_warning`` attribute. |
| 314 | |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 315 | |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 316 | .. data:: float_info |
| 317 | |
Benjamin Peterson | 2b8ef2d | 2011-04-20 18:31:22 -0500 | [diff] [blame] | 318 | A :term:`struct sequence` holding information about the float type. It |
| 319 | contains low level information about the precision and internal |
| 320 | representation. The values correspond to the various floating-point |
| 321 | constants defined in the standard header file :file:`float.h` for the 'C' |
| 322 | programming language; see section 5.2.4.2.2 of the 1999 ISO/IEC C standard |
| 323 | [C99]_, 'Characteristics of floating types', for details. |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 324 | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 325 | +---------------------+----------------+--------------------------------------------------+ |
| 326 | | attribute | float.h macro | explanation | |
| 327 | +=====================+================+==================================================+ |
Mark Dickinson | 39af05f | 2010-07-03 09:17:16 +0000 | [diff] [blame] | 328 | | :const:`epsilon` | DBL_EPSILON | difference between 1 and the least value greater | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 329 | | | | than 1 that is representable as a float | |
| 330 | +---------------------+----------------+--------------------------------------------------+ |
| 331 | | :const:`dig` | DBL_DIG | maximum number of decimal digits that can be | |
| 332 | | | | faithfully represented in a float; see below | |
| 333 | +---------------------+----------------+--------------------------------------------------+ |
| 334 | | :const:`mant_dig` | DBL_MANT_DIG | float precision: the number of base-``radix`` | |
| 335 | | | | digits in the significand of a float | |
| 336 | +---------------------+----------------+--------------------------------------------------+ |
| 337 | | :const:`max` | DBL_MAX | maximum representable finite float | |
| 338 | +---------------------+----------------+--------------------------------------------------+ |
| 339 | | :const:`max_exp` | DBL_MAX_EXP | maximum integer e such that ``radix**(e-1)`` is | |
| 340 | | | | a representable finite float | |
| 341 | +---------------------+----------------+--------------------------------------------------+ |
| 342 | | :const:`max_10_exp` | DBL_MAX_10_EXP | maximum integer e such that ``10**e`` is in the | |
| 343 | | | | range of representable finite floats | |
| 344 | +---------------------+----------------+--------------------------------------------------+ |
| 345 | | :const:`min` | DBL_MIN | minimum positive normalized float | |
| 346 | +---------------------+----------------+--------------------------------------------------+ |
| 347 | | :const:`min_exp` | DBL_MIN_EXP | minimum integer e such that ``radix**(e-1)`` is | |
| 348 | | | | a normalized float | |
| 349 | +---------------------+----------------+--------------------------------------------------+ |
| 350 | | :const:`min_10_exp` | DBL_MIN_10_EXP | minimum integer e such that ``10**e`` is a | |
| 351 | | | | normalized float | |
| 352 | +---------------------+----------------+--------------------------------------------------+ |
| 353 | | :const:`radix` | FLT_RADIX | radix of exponent representation | |
| 354 | +---------------------+----------------+--------------------------------------------------+ |
Mark Dickinson | b1e58fe | 2011-11-19 16:26:45 +0000 | [diff] [blame] | 355 | | :const:`rounds` | FLT_ROUNDS | integer constant representing the rounding mode | |
| 356 | | | | used for arithmetic operations. This reflects | |
| 357 | | | | the value of the system FLT_ROUNDS macro at | |
| 358 | | | | interpreter startup time. See section 5.2.4.2.2 | |
| 359 | | | | of the C99 standard for an explanation of the | |
| 360 | | | | possible values and their meanings. | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 361 | +---------------------+----------------+--------------------------------------------------+ |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 362 | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 363 | The attribute :attr:`sys.float_info.dig` needs further explanation. If |
| 364 | ``s`` is any string representing a decimal number with at most |
| 365 | :attr:`sys.float_info.dig` significant digits, then converting ``s`` to a |
| 366 | float and back again will recover a string representing the same decimal |
| 367 | value:: |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 368 | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 369 | >>> import sys |
| 370 | >>> sys.float_info.dig |
| 371 | 15 |
| 372 | >>> s = '3.14159265358979' # decimal string with 15 significant digits |
| 373 | >>> format(float(s), '.15g') # convert to float and back -> same value |
| 374 | '3.14159265358979' |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 375 | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 376 | But for strings with more than :attr:`sys.float_info.dig` significant digits, |
| 377 | this isn't always true:: |
| 378 | |
| 379 | >>> s = '9876543211234567' # 16 significant digits is too many! |
| 380 | >>> format(float(s), '.16g') # conversion changes value |
| 381 | '9876543211234568' |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 382 | |
Mark Dickinson | b08a53a | 2009-04-16 19:52:09 +0000 | [diff] [blame] | 383 | .. data:: float_repr_style |
| 384 | |
| 385 | A string indicating how the :func:`repr` function behaves for |
| 386 | floats. If the string has value ``'short'`` then for a finite |
| 387 | float ``x``, ``repr(x)`` aims to produce a short string with the |
| 388 | property that ``float(repr(x)) == x``. This is the usual behaviour |
| 389 | in Python 3.1 and later. Otherwise, ``float_repr_style`` has value |
| 390 | ``'legacy'`` and ``repr(x)`` behaves in the same way as it did in |
| 391 | versions of Python prior to 3.1. |
| 392 | |
| 393 | .. versionadded:: 3.1 |
| 394 | |
| 395 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 396 | .. function:: getcheckinterval() |
| 397 | |
| 398 | Return the interpreter's "check interval"; see :func:`setcheckinterval`. |
| 399 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 400 | .. deprecated:: 3.2 |
| 401 | Use :func:`getswitchinterval` instead. |
| 402 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 403 | |
| 404 | .. function:: getdefaultencoding() |
| 405 | |
| 406 | Return the name of the current default string encoding used by the Unicode |
| 407 | implementation. |
| 408 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 409 | |
| 410 | .. function:: getdlopenflags() |
| 411 | |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 412 | 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] | 413 | 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] | 414 | Availability: Unix. |
| 415 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 416 | |
| 417 | .. function:: getfilesystemencoding() |
| 418 | |
Victor Stinner | b744ba1 | 2010-05-15 12:27:16 +0000 | [diff] [blame] | 419 | Return the name of the encoding used to convert Unicode filenames into |
| 420 | system file names. The result value depends on the operating system: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 421 | |
Ezio Melotti | d5334e1 | 2010-04-29 16:24:51 +0000 | [diff] [blame] | 422 | * On Mac OS X, the encoding is ``'utf-8'``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 423 | |
| 424 | * 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] | 425 | nl_langinfo(CODESET), or ``'utf-8'`` if ``nl_langinfo(CODESET)`` failed. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 426 | |
| 427 | * On Windows NT+, file names are Unicode natively, so no conversion is |
Ezio Melotti | d5334e1 | 2010-04-29 16:24:51 +0000 | [diff] [blame] | 428 | performed. :func:`getfilesystemencoding` still returns ``'mbcs'``, as |
| 429 | this is the encoding that applications should use when they explicitly |
| 430 | want to convert Unicode strings to byte strings that are equivalent when |
| 431 | used as file names. |
| 432 | |
| 433 | * On Windows 9x, the encoding is ``'mbcs'``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 434 | |
Victor Stinner | b744ba1 | 2010-05-15 12:27:16 +0000 | [diff] [blame] | 435 | .. versionchanged:: 3.2 |
| 436 | On Unix, use ``'utf-8'`` instead of ``None`` if ``nl_langinfo(CODESET)`` |
| 437 | failed. :func:`getfilesystemencoding` result cannot be ``None``. |
| 438 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 439 | |
| 440 | .. function:: getrefcount(object) |
| 441 | |
| 442 | Return the reference count of the *object*. The count returned is generally one |
| 443 | higher than you might expect, because it includes the (temporary) reference as |
| 444 | an argument to :func:`getrefcount`. |
| 445 | |
| 446 | |
| 447 | .. function:: getrecursionlimit() |
| 448 | |
| 449 | Return the current value of the recursion limit, the maximum depth of the Python |
| 450 | interpreter stack. This limit prevents infinite recursion from causing an |
| 451 | overflow of the C stack and crashing Python. It can be set by |
| 452 | :func:`setrecursionlimit`. |
| 453 | |
| 454 | |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 455 | .. function:: getsizeof(object[, default]) |
Martin v. Löwis | 00709aa | 2008-06-04 14:18:43 +0000 | [diff] [blame] | 456 | |
| 457 | Return the size of an object in bytes. The object can be any type of |
| 458 | object. All built-in objects will return correct results, but this |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 459 | 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] | 460 | specific. |
| 461 | |
Martin v. Löwis | 1e5d0ff | 2012-06-17 10:40:16 +0200 | [diff] [blame] | 462 | Only the memory consumption directly attributed to the object is |
| 463 | accounted for, not the memory consumption of objects it refers to. |
| 464 | |
Benjamin Peterson | 4ac9ce4 | 2009-10-04 14:49:41 +0000 | [diff] [blame] | 465 | 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] | 466 | retrieve the size. Otherwise a :exc:`TypeError` will be raised. |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 467 | |
Benjamin Peterson | 4ac9ce4 | 2009-10-04 14:49:41 +0000 | [diff] [blame] | 468 | :func:`getsizeof` calls the object's ``__sizeof__`` method and adds an |
| 469 | additional garbage collector overhead if the object is managed by the garbage |
| 470 | collector. |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 471 | |
Raymond Hettinger | c539a2a | 2010-12-17 23:31:30 +0000 | [diff] [blame] | 472 | See `recursive sizeof recipe <http://code.activestate.com/recipes/577504>`_ |
| 473 | for an example of using :func:`getsizeof` recursively to find the size of |
| 474 | containers and all their contents. |
Martin v. Löwis | 00709aa | 2008-06-04 14:18:43 +0000 | [diff] [blame] | 475 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 476 | .. function:: getswitchinterval() |
| 477 | |
| 478 | Return the interpreter's "thread switch interval"; see |
| 479 | :func:`setswitchinterval`. |
| 480 | |
Antoine Pitrou | 79707ca | 2009-11-11 22:03:32 +0000 | [diff] [blame] | 481 | .. versionadded:: 3.2 |
| 482 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 483 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 484 | .. function:: _getframe([depth]) |
| 485 | |
| 486 | Return a frame object from the call stack. If optional integer *depth* is |
| 487 | given, return the frame object that many calls below the top of the stack. If |
| 488 | that is deeper than the call stack, :exc:`ValueError` is raised. The default |
| 489 | for *depth* is zero, returning the frame at the top of the call stack. |
| 490 | |
Georg Brandl | 495f7b5 | 2009-10-27 15:28:25 +0000 | [diff] [blame] | 491 | .. impl-detail:: |
| 492 | |
| 493 | This function should be used for internal and specialized purposes only. |
| 494 | It is not guaranteed to exist in all implementations of Python. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 495 | |
| 496 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 497 | .. function:: getprofile() |
| 498 | |
| 499 | .. index:: |
| 500 | single: profile function |
| 501 | single: profiler |
| 502 | |
| 503 | Get the profiler function as set by :func:`setprofile`. |
| 504 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 505 | |
| 506 | .. function:: gettrace() |
| 507 | |
| 508 | .. index:: |
| 509 | single: trace function |
| 510 | single: debugger |
| 511 | |
| 512 | Get the trace function as set by :func:`settrace`. |
| 513 | |
Georg Brandl | 495f7b5 | 2009-10-27 15:28:25 +0000 | [diff] [blame] | 514 | .. impl-detail:: |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 515 | |
| 516 | The :func:`gettrace` function is intended only for implementing debuggers, |
Georg Brandl | 495f7b5 | 2009-10-27 15:28:25 +0000 | [diff] [blame] | 517 | profilers, coverage tools and the like. Its behavior is part of the |
| 518 | implementation platform, rather than part of the language definition, and |
| 519 | thus may not be available in all Python implementations. |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 520 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 521 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 522 | .. function:: getwindowsversion() |
| 523 | |
Eric Smith | 7338a39 | 2010-01-27 00:56:30 +0000 | [diff] [blame] | 524 | Return a named tuple describing the Windows version |
Eric Smith | f7bb578 | 2010-01-27 00:44:57 +0000 | [diff] [blame] | 525 | currently running. The named elements are *major*, *minor*, |
| 526 | *build*, *platform*, *service_pack*, *service_pack_minor*, |
| 527 | *service_pack_major*, *suite_mask*, and *product_type*. |
| 528 | *service_pack* contains a string while all other values are |
| 529 | integers. The components can also be accessed by name, so |
| 530 | ``sys.getwindowsversion()[0]`` is equivalent to |
| 531 | ``sys.getwindowsversion().major``. For compatibility with prior |
| 532 | versions, only the first 5 elements are retrievable by indexing. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 533 | |
| 534 | *platform* may be one of the following values: |
| 535 | |
Christian Heimes | 81ee3ef | 2008-05-04 22:42:01 +0000 | [diff] [blame] | 536 | +-----------------------------------------+-------------------------+ |
| 537 | | Constant | Platform | |
| 538 | +=========================================+=========================+ |
| 539 | | :const:`0 (VER_PLATFORM_WIN32s)` | Win32s on Windows 3.1 | |
| 540 | +-----------------------------------------+-------------------------+ |
| 541 | | :const:`1 (VER_PLATFORM_WIN32_WINDOWS)` | Windows 95/98/ME | |
| 542 | +-----------------------------------------+-------------------------+ |
| 543 | | :const:`2 (VER_PLATFORM_WIN32_NT)` | Windows NT/2000/XP/x64 | |
| 544 | +-----------------------------------------+-------------------------+ |
| 545 | | :const:`3 (VER_PLATFORM_WIN32_CE)` | Windows CE | |
| 546 | +-----------------------------------------+-------------------------+ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 547 | |
Eric Smith | f7bb578 | 2010-01-27 00:44:57 +0000 | [diff] [blame] | 548 | *product_type* may be one of the following values: |
| 549 | |
| 550 | +---------------------------------------+---------------------------------+ |
| 551 | | Constant | Meaning | |
| 552 | +=======================================+=================================+ |
| 553 | | :const:`1 (VER_NT_WORKSTATION)` | The system is a workstation. | |
| 554 | +---------------------------------------+---------------------------------+ |
| 555 | | :const:`2 (VER_NT_DOMAIN_CONTROLLER)` | The system is a domain | |
| 556 | | | controller. | |
| 557 | +---------------------------------------+---------------------------------+ |
| 558 | | :const:`3 (VER_NT_SERVER)` | The system is a server, but not | |
| 559 | | | a domain controller. | |
| 560 | +---------------------------------------+---------------------------------+ |
| 561 | |
| 562 | |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 563 | This function wraps the Win32 :c:func:`GetVersionEx` function; see the |
| 564 | Microsoft documentation on :c:func:`OSVERSIONINFOEX` for more information |
Eric Smith | f7bb578 | 2010-01-27 00:44:57 +0000 | [diff] [blame] | 565 | about these fields. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 566 | |
| 567 | Availability: Windows. |
| 568 | |
Ezio Melotti | 83fc6dd | 2010-01-27 22:44:03 +0000 | [diff] [blame] | 569 | .. versionchanged:: 3.2 |
Eric Smith | f7bb578 | 2010-01-27 00:44:57 +0000 | [diff] [blame] | 570 | Changed to a named tuple and added *service_pack_minor*, |
| 571 | *service_pack_major*, *suite_mask*, and *product_type*. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 572 | |
Mark Dickinson | dc787d2 | 2010-05-23 13:33:13 +0000 | [diff] [blame] | 573 | |
| 574 | .. data:: hash_info |
| 575 | |
Benjamin Peterson | 2b8ef2d | 2011-04-20 18:31:22 -0500 | [diff] [blame] | 576 | A :term:`struct sequence` giving parameters of the numeric hash |
| 577 | implementation. For more details about hashing of numeric types, see |
| 578 | :ref:`numeric-hash`. |
Mark Dickinson | dc787d2 | 2010-05-23 13:33:13 +0000 | [diff] [blame] | 579 | |
| 580 | +---------------------+--------------------------------------------------+ |
| 581 | | attribute | explanation | |
| 582 | +=====================+==================================================+ |
| 583 | | :const:`width` | width in bits used for hash values | |
| 584 | +---------------------+--------------------------------------------------+ |
| 585 | | :const:`modulus` | prime modulus P used for numeric hash scheme | |
| 586 | +---------------------+--------------------------------------------------+ |
| 587 | | :const:`inf` | hash value returned for a positive infinity | |
| 588 | +---------------------+--------------------------------------------------+ |
| 589 | | :const:`nan` | hash value returned for a nan | |
| 590 | +---------------------+--------------------------------------------------+ |
| 591 | | :const:`imag` | multiplier used for the imaginary part of a | |
| 592 | | | complex number | |
| 593 | +---------------------+--------------------------------------------------+ |
| 594 | |
| 595 | .. versionadded:: 3.2 |
| 596 | |
| 597 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 598 | .. data:: hexversion |
| 599 | |
| 600 | The version number encoded as a single integer. This is guaranteed to increase |
| 601 | with each version, including proper support for non-production releases. For |
| 602 | example, to test that the Python interpreter is at least version 1.5.2, use:: |
| 603 | |
| 604 | if sys.hexversion >= 0x010502F0: |
| 605 | # use some advanced feature |
| 606 | ... |
| 607 | else: |
| 608 | # use an alternative implementation or warn the user |
| 609 | ... |
| 610 | |
| 611 | This is called ``hexversion`` since it only really looks meaningful when viewed |
| 612 | 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] | 613 | :term:`struct sequence` :data:`sys.version_info` may be used for a more |
| 614 | human-friendly encoding of the same information. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 615 | |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 616 | The ``hexversion`` is a 32-bit number with the following layout: |
R David Murray | 2043f9c | 2011-04-25 16:12:26 -0400 | [diff] [blame] | 617 | |
| 618 | +-------------------------+------------------------------------------------+ |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 619 | | Bits (big endian order) | Meaning | |
R David Murray | 2043f9c | 2011-04-25 16:12:26 -0400 | [diff] [blame] | 620 | +=========================+================================================+ |
| 621 | | :const:`1-8` | ``PY_MAJOR_VERSION`` (the ``2`` in | |
| 622 | | | ``2.1.0a3``) | |
| 623 | +-------------------------+------------------------------------------------+ |
| 624 | | :const:`9-16` | ``PY_MINOR_VERSION`` (the ``1`` in | |
| 625 | | | ``2.1.0a3``) | |
| 626 | +-------------------------+------------------------------------------------+ |
| 627 | | :const:`17-24` | ``PY_MICRO_VERSION`` (the ``0`` in | |
| 628 | | | ``2.1.0a3``) | |
| 629 | +-------------------------+------------------------------------------------+ |
| 630 | | :const:`25-28` | ``PY_RELEASE_LEVEL`` (``0xA`` for alpha, | |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 631 | | | ``0xB`` for beta, ``0xC`` for release | |
| 632 | | | candidate and ``0xF`` for final) | |
R David Murray | 2043f9c | 2011-04-25 16:12:26 -0400 | [diff] [blame] | 633 | +-------------------------+------------------------------------------------+ |
| 634 | | :const:`29-32` | ``PY_RELEASE_SERIAL`` (the ``3`` in | |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 635 | | | ``2.1.0a3``, zero for final releases) | |
R David Murray | 2043f9c | 2011-04-25 16:12:26 -0400 | [diff] [blame] | 636 | +-------------------------+------------------------------------------------+ |
| 637 | |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 638 | Thus ``2.1.0a3`` is hexversion ``0x020100a3``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 639 | |
Barry Warsaw | 409da15 | 2012-06-03 16:18:47 -0400 | [diff] [blame] | 640 | |
| 641 | .. data:: implementation |
| 642 | |
Barry Warsaw | 9b10e1f | 2012-06-04 11:06:45 -0400 | [diff] [blame] | 643 | An object containing information about the implementation of the |
| 644 | currently running Python interpreter. The following attributes are |
| 645 | required to exist in all Python implementations. |
Barry Warsaw | 409da15 | 2012-06-03 16:18:47 -0400 | [diff] [blame] | 646 | |
Barry Warsaw | 9b10e1f | 2012-06-04 11:06:45 -0400 | [diff] [blame] | 647 | *name* is the implementation's identifier, e.g. ``'cpython'``. The actual |
| 648 | string is defined by the Python implementation, but it is guaranteed to be |
| 649 | lower case. |
Barry Warsaw | 409da15 | 2012-06-03 16:18:47 -0400 | [diff] [blame] | 650 | |
| 651 | *version* is a named tuple, in the same format as |
| 652 | :data:`sys.version_info`. It represents the version of the Python |
| 653 | *implementation*. This has a distinct meaning from the specific |
| 654 | version of the Python *language* to which the currently running |
| 655 | interpreter conforms, which ``sys.version_info`` represents. For |
| 656 | example, for PyPy 1.8 ``sys.implementation.version`` might be |
| 657 | ``sys.version_info(1, 8, 0, 'final', 0)``, whereas ``sys.version_info`` |
Barry Warsaw | 9b10e1f | 2012-06-04 11:06:45 -0400 | [diff] [blame] | 658 | would be ``sys.version_info(2, 7, 2, 'final', 0)``. For CPython they |
Barry Warsaw | 409da15 | 2012-06-03 16:18:47 -0400 | [diff] [blame] | 659 | are the same value, since it is the reference implementation. |
| 660 | |
| 661 | *hexversion* is the implementation version in hexadecimal format, like |
| 662 | :data:`sys.hexversion`. |
| 663 | |
| 664 | *cache_tag* is the tag used by the import machinery in the filenames of |
| 665 | cached modules. By convention, it would be a composite of the |
| 666 | implementation's name and version, like ``'cpython-33'``. However, a |
| 667 | Python implementation may use some other value if appropriate. If |
| 668 | ``cache_tag`` is set to ``None``, it indicates that module caching should |
| 669 | be disabled. |
| 670 | |
Barry Warsaw | 9b10e1f | 2012-06-04 11:06:45 -0400 | [diff] [blame] | 671 | :data:`sys.implementation` may contain additional attributes specific to |
| 672 | the Python implementation. These non-standard attributes must start with |
| 673 | an underscore, and are not described here. Regardless of its contents, |
| 674 | :data:`sys.implementation` will not change during a run of the interpreter, |
| 675 | nor between implementation versions. (It may change between Python |
| 676 | language versions, however.) See `PEP 421` for more information. |
Barry Warsaw | 409da15 | 2012-06-03 16:18:47 -0400 | [diff] [blame] | 677 | |
| 678 | .. versionadded:: 3.3 |
| 679 | |
| 680 | |
Mark Dickinson | bd79264 | 2009-03-18 20:06:12 +0000 | [diff] [blame] | 681 | .. data:: int_info |
| 682 | |
Benjamin Peterson | 2b8ef2d | 2011-04-20 18:31:22 -0500 | [diff] [blame] | 683 | A :term:`struct sequence` that holds information about Python's internal |
| 684 | representation of integers. The attributes are read only. |
Mark Dickinson | bd79264 | 2009-03-18 20:06:12 +0000 | [diff] [blame] | 685 | |
| 686 | +-------------------------+----------------------------------------------+ |
R David Murray | 9beb34e | 2011-04-30 16:35:29 -0400 | [diff] [blame] | 687 | | Attribute | Explanation | |
Mark Dickinson | bd79264 | 2009-03-18 20:06:12 +0000 | [diff] [blame] | 688 | +=========================+==============================================+ |
| 689 | | :const:`bits_per_digit` | number of bits held in each digit. Python | |
| 690 | | | integers are stored internally in base | |
| 691 | | | ``2**int_info.bits_per_digit`` | |
| 692 | +-------------------------+----------------------------------------------+ |
| 693 | | :const:`sizeof_digit` | size in bytes of the C type used to | |
| 694 | | | represent a digit | |
| 695 | +-------------------------+----------------------------------------------+ |
| 696 | |
Mark Dickinson | d72c7b6 | 2009-03-20 16:00:49 +0000 | [diff] [blame] | 697 | .. versionadded:: 3.1 |
| 698 | |
Mark Dickinson | bd79264 | 2009-03-18 20:06:12 +0000 | [diff] [blame] | 699 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 700 | .. function:: intern(string) |
| 701 | |
| 702 | Enter *string* in the table of "interned" strings and return the interned string |
| 703 | -- which is *string* itself or a copy. Interning strings is useful to gain a |
| 704 | little performance on dictionary lookup -- if the keys in a dictionary are |
| 705 | interned, and the lookup key is interned, the key comparisons (after hashing) |
| 706 | can be done by a pointer compare instead of a string compare. Normally, the |
| 707 | names used in Python programs are automatically interned, and the dictionaries |
| 708 | used to hold module, class or instance attributes have interned keys. |
| 709 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 710 | Interned strings are not immortal; you must keep a reference to the return |
| 711 | value of :func:`intern` around to benefit from it. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 712 | |
| 713 | |
| 714 | .. data:: last_type |
| 715 | last_value |
| 716 | last_traceback |
| 717 | |
| 718 | These three variables are not always defined; they are set when an exception is |
| 719 | not handled and the interpreter prints an error message and a stack traceback. |
| 720 | Their intended use is to allow an interactive user to import a debugger module |
| 721 | and engage in post-mortem debugging without having to re-execute the command |
| 722 | 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] | 723 | post-mortem debugger; see :mod:`pdb` module for |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 724 | more information.) |
| 725 | |
| 726 | 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] | 727 | :func:`exc_info` above. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 728 | |
| 729 | |
Christian Heimes | a37d4c6 | 2007-12-04 23:02:19 +0000 | [diff] [blame] | 730 | .. data:: maxsize |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 731 | |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 732 | 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] | 733 | take. It's usually ``2**31 - 1`` on a 32-bit platform and ``2**63 - 1`` on a |
| 734 | 64-bit platform. |
Christian Heimes | a37d4c6 | 2007-12-04 23:02:19 +0000 | [diff] [blame] | 735 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 736 | |
| 737 | .. data:: maxunicode |
| 738 | |
Ezio Melotti | 48a2f8f | 2011-09-29 00:18:19 +0300 | [diff] [blame] | 739 | An integer giving the value of the largest Unicode code point, |
| 740 | i.e. ``1114111`` (``0x10FFFF`` in hexadecimal). |
| 741 | |
| 742 | .. versionchanged:: 3.3 |
Éric Araujo | 525b1e9 | 2011-10-05 01:06:31 +0200 | [diff] [blame] | 743 | Before :pep:`393`, ``sys.maxunicode`` used to be either ``0xFFFF`` |
Ezio Melotti | 48a2f8f | 2011-09-29 00:18:19 +0300 | [diff] [blame] | 744 | or ``0x10FFFF``, depending on the configuration option that specified |
| 745 | whether Unicode characters were stored as UCS-2 or UCS-4. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 746 | |
| 747 | |
Brett Cannon | e43b060 | 2009-03-21 03:11:16 +0000 | [diff] [blame] | 748 | .. data:: meta_path |
| 749 | |
| 750 | A list of :term:`finder` objects that have their :meth:`find_module` |
| 751 | methods called to see if one of the objects can find the module to be |
| 752 | imported. The :meth:`find_module` method is called at least with the |
| 753 | absolute name of the module being imported. If the module to be imported is |
| 754 | contained in package then the parent package's :attr:`__path__` attribute |
Georg Brandl | 375aec2 | 2011-01-15 17:03:02 +0000 | [diff] [blame] | 755 | is passed in as a second argument. The method returns ``None`` if |
Brett Cannon | e43b060 | 2009-03-21 03:11:16 +0000 | [diff] [blame] | 756 | the module cannot be found, else returns a :term:`loader`. |
| 757 | |
| 758 | :data:`sys.meta_path` is searched before any implicit default finders or |
| 759 | :data:`sys.path`. |
| 760 | |
| 761 | See :pep:`302` for the original specification. |
| 762 | |
| 763 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 764 | .. data:: modules |
| 765 | |
| 766 | This is a dictionary that maps module names to modules which have already been |
| 767 | loaded. This can be manipulated to force reloading of modules and other tricks. |
| 768 | |
| 769 | |
| 770 | .. data:: path |
| 771 | |
| 772 | .. index:: triple: module; search; path |
| 773 | |
| 774 | A list of strings that specifies the search path for modules. Initialized from |
| 775 | the environment variable :envvar:`PYTHONPATH`, plus an installation-dependent |
| 776 | default. |
| 777 | |
| 778 | As initialized upon program startup, the first item of this list, ``path[0]``, |
| 779 | is the directory containing the script that was used to invoke the Python |
| 780 | interpreter. If the script directory is not available (e.g. if the interpreter |
| 781 | is invoked interactively or if the script is read from standard input), |
| 782 | ``path[0]`` is the empty string, which directs Python to search modules in the |
| 783 | current directory first. Notice that the script directory is inserted *before* |
| 784 | the entries inserted as a result of :envvar:`PYTHONPATH`. |
| 785 | |
| 786 | A program is free to modify this list for its own purposes. |
| 787 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 788 | |
Benjamin Peterson | 058e31e | 2009-01-16 03:54:08 +0000 | [diff] [blame] | 789 | .. seealso:: |
| 790 | Module :mod:`site` This describes how to use .pth files to extend |
| 791 | :data:`sys.path`. |
| 792 | |
| 793 | |
Brett Cannon | e43b060 | 2009-03-21 03:11:16 +0000 | [diff] [blame] | 794 | .. data:: path_hooks |
| 795 | |
| 796 | A list of callables that take a path argument to try to create a |
| 797 | :term:`finder` for the path. If a finder can be created, it is to be |
| 798 | returned by the callable, else raise :exc:`ImportError`. |
| 799 | |
| 800 | Originally specified in :pep:`302`. |
| 801 | |
| 802 | |
| 803 | .. data:: path_importer_cache |
| 804 | |
| 805 | A dictionary acting as a cache for :term:`finder` objects. The keys are |
| 806 | paths that have been passed to :data:`sys.path_hooks` and the values are |
| 807 | 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] | 808 | explicit finder is found on :data:`sys.path_hooks` then ``None`` is |
Brett Cannon | e43b060 | 2009-03-21 03:11:16 +0000 | [diff] [blame] | 809 | stored to represent the implicit default finder should be used. If the path |
| 810 | is not an existing path then :class:`imp.NullImporter` is set. |
| 811 | |
| 812 | Originally specified in :pep:`302`. |
| 813 | |
| 814 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 815 | .. data:: platform |
| 816 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 817 | This string contains a platform identifier that can be used to append |
| 818 | platform-specific components to :data:`sys.path`, for instance. |
| 819 | |
Victor Stinner | 795eaeb | 2011-08-21 12:08:11 +0200 | [diff] [blame] | 820 | For Unix systems, except on Linux, this is the lowercased OS name as |
| 821 | returned by ``uname -s`` with the first part of the version as returned by |
| 822 | ``uname -r`` appended, e.g. ``'sunos5'`` or ``'freebsd8'``, *at the time |
| 823 | when Python was built*. Unless you want to test for a specific system |
| 824 | version, it is therefore recommended to use the following idiom:: |
Antoine Pitrou | a83cdaa | 2011-07-09 15:54:23 +0200 | [diff] [blame] | 825 | |
Victor Stinner | 795eaeb | 2011-08-21 12:08:11 +0200 | [diff] [blame] | 826 | if sys.platform.startswith('freebsd'): |
| 827 | # FreeBSD-specific code here... |
Georg Brandl | a47e53e | 2011-09-03 09:26:09 +0200 | [diff] [blame] | 828 | elif sys.platform.startswith('linux'): |
Antoine Pitrou | a83cdaa | 2011-07-09 15:54:23 +0200 | [diff] [blame] | 829 | # Linux-specific code here... |
| 830 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 831 | For other systems, the values are: |
| 832 | |
| 833 | ================ =========================== |
| 834 | System :data:`platform` value |
| 835 | ================ =========================== |
Victor Stinner | 795eaeb | 2011-08-21 12:08:11 +0200 | [diff] [blame] | 836 | Linux ``'linux'`` |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 837 | Windows ``'win32'`` |
| 838 | Windows/Cygwin ``'cygwin'`` |
Georg Brandl | c575c90 | 2008-09-13 17:46:05 +0000 | [diff] [blame] | 839 | Mac OS X ``'darwin'`` |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 840 | ================ =========================== |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 841 | |
Victor Stinner | 795eaeb | 2011-08-21 12:08:11 +0200 | [diff] [blame] | 842 | .. versionchanged:: 3.3 |
| 843 | On Linux, :attr:`sys.platform` doesn't contain the major version anymore. |
Georg Brandl | fbd1e04 | 2011-09-04 08:42:26 +0200 | [diff] [blame] | 844 | It is always ``'linux'``, instead of ``'linux2'`` or ``'linux3'``. Since |
| 845 | older Python versions include the version number, it is recommended to |
| 846 | always use the ``startswith`` idiom presented above. |
Victor Stinner | 795eaeb | 2011-08-21 12:08:11 +0200 | [diff] [blame] | 847 | |
Antoine Pitrou | a83cdaa | 2011-07-09 15:54:23 +0200 | [diff] [blame] | 848 | .. seealso:: |
Georg Brandl | eb25fb7 | 2012-02-23 21:12:39 +0100 | [diff] [blame] | 849 | |
Antoine Pitrou | a83cdaa | 2011-07-09 15:54:23 +0200 | [diff] [blame] | 850 | :attr:`os.name` has a coarser granularity. :func:`os.uname` gives |
| 851 | system-dependent version information. |
| 852 | |
| 853 | The :mod:`platform` module provides detailed checks for the |
| 854 | system's identity. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 855 | |
Georg Brandl | fbd1e04 | 2011-09-04 08:42:26 +0200 | [diff] [blame] | 856 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 857 | .. data:: prefix |
| 858 | |
| 859 | A string giving the site-specific directory prefix where the platform |
| 860 | independent Python files are installed; by default, this is the string |
Éric Araujo | 713d303 | 2010-11-18 16:38:46 +0000 | [diff] [blame] | 861 | ``'/usr/local'``. This can be set at build time with the ``--prefix`` |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 862 | argument to the :program:`configure` script. The main collection of Python |
Georg Brandl | a673eb8 | 2012-03-04 16:17:05 +0100 | [diff] [blame] | 863 | 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] | 864 | while the platform independent header files (all except :file:`pyconfig.h`) are |
Georg Brandl | eb25fb7 | 2012-02-23 21:12:39 +0100 | [diff] [blame] | 865 | 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] | 866 | number of Python, for example ``3.2``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 867 | |
Vinay Sajip | cd9b746 | 2012-07-09 10:37:01 +0100 | [diff] [blame] | 868 | .. note:: If a :ref:`virtual environment <venv-def>` is in effect, this |
| 869 | value will be changed in ``site.py`` to point to the virtual |
| 870 | environment. The value for the Python installation will still be |
| 871 | available, via :data:`base_prefix`. |
Vinay Sajip | 7ded1f0 | 2012-05-26 03:45:29 +0100 | [diff] [blame] | 872 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 873 | |
| 874 | .. data:: ps1 |
| 875 | ps2 |
| 876 | |
| 877 | .. index:: |
| 878 | single: interpreter prompts |
| 879 | single: prompts, interpreter |
| 880 | |
| 881 | Strings specifying the primary and secondary prompt of the interpreter. These |
| 882 | are only defined if the interpreter is in interactive mode. Their initial |
| 883 | values in this case are ``'>>> '`` and ``'... '``. If a non-string object is |
| 884 | assigned to either variable, its :func:`str` is re-evaluated each time the |
| 885 | interpreter prepares to read a new interactive command; this can be used to |
| 886 | implement a dynamic prompt. |
| 887 | |
| 888 | |
| 889 | .. function:: setcheckinterval(interval) |
| 890 | |
| 891 | Set the interpreter's "check interval". This integer value determines how often |
| 892 | the interpreter checks for periodic things such as thread switches and signal |
| 893 | handlers. The default is ``100``, meaning the check is performed every 100 |
| 894 | Python virtual instructions. Setting it to a larger value may increase |
| 895 | performance for programs using threads. Setting it to a value ``<=`` 0 checks |
| 896 | every virtual instruction, maximizing responsiveness as well as overhead. |
| 897 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 898 | .. deprecated:: 3.2 |
Georg Brandl | 67b21b7 | 2010-08-17 15:07:14 +0000 | [diff] [blame] | 899 | This function doesn't have an effect anymore, as the internal logic for |
| 900 | thread switching and asynchronous tasks has been rewritten. Use |
| 901 | :func:`setswitchinterval` instead. |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 902 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 903 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 904 | .. function:: setdlopenflags(n) |
| 905 | |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 906 | 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] | 907 | the interpreter loads extension modules. Among other things, this will enable a |
| 908 | lazy resolving of symbols when importing a module, if called as |
| 909 | ``sys.setdlopenflags(0)``. To share symbols across extension modules, call as |
Victor Stinner | 8b905bd | 2011-10-25 13:34:04 +0200 | [diff] [blame] | 910 | ``sys.setdlopenflags(os.RTLD_GLOBAL)``. Symbolic names for the flag modules |
| 911 | can be found in the :mod:`os` module (``RTLD_xxx`` constants, e.g. |
| 912 | :data:`os.RTLD_LAZY`). |
| 913 | |
| 914 | Availability: Unix. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 915 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 916 | .. function:: setprofile(profilefunc) |
| 917 | |
| 918 | .. index:: |
| 919 | single: profile function |
| 920 | single: profiler |
| 921 | |
| 922 | Set the system's profile function, which allows you to implement a Python source |
| 923 | code profiler in Python. See chapter :ref:`profile` for more information on the |
| 924 | Python profiler. The system's profile function is called similarly to the |
| 925 | system's trace function (see :func:`settrace`), but it isn't called for each |
| 926 | executed line of code (only on call and return, but the return event is reported |
| 927 | even when an exception has been set). The function is thread-specific, but |
| 928 | there is no way for the profiler to know about context switches between threads, |
| 929 | so it does not make sense to use this in the presence of multiple threads. Also, |
| 930 | its return value is not used, so it can simply return ``None``. |
| 931 | |
| 932 | |
| 933 | .. function:: setrecursionlimit(limit) |
| 934 | |
| 935 | Set the maximum depth of the Python interpreter stack to *limit*. This limit |
| 936 | prevents infinite recursion from causing an overflow of the C stack and crashing |
| 937 | Python. |
| 938 | |
| 939 | 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] | 940 | 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] | 941 | that supports a higher limit. This should be done with care, because a too-high |
| 942 | limit can lead to a crash. |
| 943 | |
| 944 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 945 | .. function:: setswitchinterval(interval) |
| 946 | |
| 947 | Set the interpreter's thread switch interval (in seconds). This floating-point |
| 948 | value determines the ideal duration of the "timeslices" allocated to |
| 949 | concurrently running Python threads. Please note that the actual value |
| 950 | can be higher, especially if long-running internal functions or methods |
| 951 | are used. Also, which thread becomes scheduled at the end of the interval |
| 952 | is the operating system's decision. The interpreter doesn't have its |
| 953 | own scheduler. |
| 954 | |
Antoine Pitrou | 79707ca | 2009-11-11 22:03:32 +0000 | [diff] [blame] | 955 | .. versionadded:: 3.2 |
| 956 | |
Antoine Pitrou | d42bc51 | 2009-11-10 23:18:31 +0000 | [diff] [blame] | 957 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 958 | .. function:: settrace(tracefunc) |
| 959 | |
| 960 | .. index:: |
| 961 | single: trace function |
| 962 | single: debugger |
| 963 | |
| 964 | 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] | 965 | source code debugger in Python. The function is thread-specific; for a |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 966 | debugger to support multiple threads, it must be registered using |
| 967 | :func:`settrace` for each thread being debugged. |
| 968 | |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 969 | Trace functions should have three arguments: *frame*, *event*, and |
| 970 | *arg*. *frame* is the current stack frame. *event* is a string: ``'call'``, |
| 971 | ``'line'``, ``'return'``, ``'exception'``, ``'c_call'``, ``'c_return'``, or |
| 972 | ``'c_exception'``. *arg* depends on the event type. |
| 973 | |
| 974 | The trace function is invoked (with *event* set to ``'call'``) whenever a new |
| 975 | local scope is entered; it should return a reference to a local trace |
| 976 | function to be used that scope, or ``None`` if the scope shouldn't be traced. |
| 977 | |
| 978 | The local trace function should return a reference to itself (or to another |
| 979 | function for further tracing in that scope), or ``None`` to turn off tracing |
| 980 | in that scope. |
| 981 | |
| 982 | The events have the following meaning: |
| 983 | |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 984 | ``'call'`` |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 985 | A function is called (or some other code block entered). The |
| 986 | global trace function is called; *arg* is ``None``; the return value |
| 987 | specifies the local trace function. |
| 988 | |
| 989 | ``'line'`` |
Alexandre Vassalotti | 7b82b40 | 2009-07-21 04:30:03 +0000 | [diff] [blame] | 990 | The interpreter is about to execute a new line of code or re-execute the |
| 991 | condition of a loop. The local trace function is called; *arg* is |
| 992 | ``None``; the return value specifies the new local trace function. See |
| 993 | :file:`Objects/lnotab_notes.txt` for a detailed explanation of how this |
| 994 | works. |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 995 | |
| 996 | ``'return'`` |
| 997 | 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] | 998 | function is called; *arg* is the value that will be returned, or ``None`` |
| 999 | if the event is caused by an exception being raised. The trace function's |
| 1000 | return value is ignored. |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 1001 | |
| 1002 | ``'exception'`` |
| 1003 | An exception has occurred. The local trace function is called; *arg* is a |
| 1004 | tuple ``(exception, value, traceback)``; the return value specifies the |
| 1005 | new local trace function. |
| 1006 | |
| 1007 | ``'c_call'`` |
| 1008 | 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] | 1009 | a built-in. *arg* is the C function object. |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 1010 | |
| 1011 | ``'c_return'`` |
Georg Brandl | d0b0e1d | 2010-10-15 16:42:37 +0000 | [diff] [blame] | 1012 | 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] | 1013 | |
| 1014 | ``'c_exception'`` |
Georg Brandl | d0b0e1d | 2010-10-15 16:42:37 +0000 | [diff] [blame] | 1015 | 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] | 1016 | |
| 1017 | Note that as an exception is propagated down the chain of callers, an |
| 1018 | ``'exception'`` event is generated at each level. |
| 1019 | |
| 1020 | For more information on code and frame objects, refer to :ref:`types`. |
| 1021 | |
Georg Brandl | 495f7b5 | 2009-10-27 15:28:25 +0000 | [diff] [blame] | 1022 | .. impl-detail:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1023 | |
| 1024 | The :func:`settrace` function is intended only for implementing debuggers, |
Georg Brandl | 495f7b5 | 2009-10-27 15:28:25 +0000 | [diff] [blame] | 1025 | profilers, coverage tools and the like. Its behavior is part of the |
| 1026 | implementation platform, rather than part of the language definition, and |
| 1027 | thus may not be available in all Python implementations. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1028 | |
| 1029 | |
| 1030 | .. function:: settscdump(on_flag) |
| 1031 | |
| 1032 | Activate dumping of VM measurements using the Pentium timestamp counter, if |
| 1033 | *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] | 1034 | available only if Python was compiled with ``--with-tsc``. To understand |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1035 | the output of this dump, read :file:`Python/ceval.c` in the Python sources. |
| 1036 | |
Benjamin Peterson | 21896a3 | 2010-03-21 22:03:03 +0000 | [diff] [blame] | 1037 | .. impl-detail:: |
| 1038 | This function is intimately bound to CPython implementation details and |
| 1039 | thus not likely to be implemented elsewhere. |
| 1040 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1041 | |
| 1042 | .. data:: stdin |
| 1043 | stdout |
| 1044 | stderr |
| 1045 | |
Antoine Pitrou | 7158e06 | 2011-12-15 16:25:34 +0100 | [diff] [blame] | 1046 | :term:`File objects <file object>` used by the interpreter for standard |
| 1047 | input, output and errors: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1048 | |
Antoine Pitrou | 7158e06 | 2011-12-15 16:25:34 +0100 | [diff] [blame] | 1049 | * ``stdin`` is used for all interactive input (including calls to |
| 1050 | :func:`input`); |
| 1051 | * ``stdout`` is used for the output of :func:`print` and :term:`expression` |
| 1052 | statements and for the prompts of :func:`input`; |
| 1053 | * The interpreter's own prompts and its error messages go to ``stderr``. |
| 1054 | |
| 1055 | By default, these streams are regular text streams as returned by the |
| 1056 | :func:`open` function. Their parameters are chosen as follows: |
| 1057 | |
| 1058 | * The character encoding is platform-dependent. Under Windows, if the stream |
| 1059 | is interactive (that is, if its :meth:`isatty` method returns True), the |
| 1060 | console codepage is used, otherwise the ANSI code page. Under other |
| 1061 | platforms, the locale encoding is used (see :meth:`locale.getpreferredencoding`). |
| 1062 | |
| 1063 | Under all platforms though, you can override this value by setting the |
| 1064 | :envvar:`PYTHONIOENCODING` environment variable. |
| 1065 | |
| 1066 | * When interactive, standard streams are line-buffered. Otherwise, they |
| 1067 | are block-buffered like regular text files. You can override this |
| 1068 | value with the :option:`-u` command-line option. |
| 1069 | |
| 1070 | To write or read binary data from/to the standard streams, use the |
| 1071 | underlying binary :data:`~io.TextIOBase.buffer`. For example, to write |
| 1072 | bytes to :data:`stdout`, use ``sys.stdout.buffer.write(b'abc')``. Using |
| 1073 | :meth:`io.TextIOBase.detach`, streams can be made binary by default. This |
Benjamin Peterson | 995bb47 | 2009-06-14 18:41:18 +0000 | [diff] [blame] | 1074 | function sets :data:`stdin` and :data:`stdout` to binary:: |
Benjamin Peterson | 4199d60 | 2009-05-12 20:47:57 +0000 | [diff] [blame] | 1075 | |
| 1076 | def make_streams_binary(): |
| 1077 | sys.stdin = sys.stdin.detach() |
Benjamin Peterson | 4487f53 | 2009-05-13 21:15:03 +0000 | [diff] [blame] | 1078 | sys.stdout = sys.stdout.detach() |
Benjamin Peterson | 995bb47 | 2009-06-14 18:41:18 +0000 | [diff] [blame] | 1079 | |
Antoine Pitrou | 7158e06 | 2011-12-15 16:25:34 +0100 | [diff] [blame] | 1080 | Note that the streams may be replaced with objects (like :class:`io.StringIO`) |
| 1081 | that do not support the :attr:`~io.BufferedIOBase.buffer` attribute or the |
Benjamin Peterson | 995bb47 | 2009-06-14 18:41:18 +0000 | [diff] [blame] | 1082 | :meth:`~io.BufferedIOBase.detach` method and can raise :exc:`AttributeError` |
| 1083 | or :exc:`io.UnsupportedOperation`. |
Benjamin Peterson | eb9fc52 | 2008-12-07 14:58:03 +0000 | [diff] [blame] | 1084 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1085 | |
| 1086 | .. data:: __stdin__ |
| 1087 | __stdout__ |
| 1088 | __stderr__ |
| 1089 | |
| 1090 | These objects contain the original values of ``stdin``, ``stderr`` and |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 1091 | ``stdout`` at the start of the program. They are used during finalization, |
| 1092 | and could be useful to print to the actual standard stream no matter if the |
| 1093 | ``sys.std*`` object has been redirected. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1094 | |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 1095 | It can also be used to restore the actual files to known working file objects |
| 1096 | in case they have been overwritten with a broken object. However, the |
| 1097 | preferred way to do this is to explicitly save the previous stream before |
| 1098 | replacing it, and restore the saved object. |
Christian Heimes | 58cb1b8 | 2007-11-13 02:19:40 +0000 | [diff] [blame] | 1099 | |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 1100 | .. note:: |
| 1101 | Under some conditions ``stdin``, ``stdout`` and ``stderr`` as well as the |
| 1102 | original values ``__stdin__``, ``__stdout__`` and ``__stderr__`` can be |
| 1103 | None. It is usually the case for Windows GUI apps that aren't connected |
| 1104 | to a console and Python apps started with :program:`pythonw`. |
Christian Heimes | 58cb1b8 | 2007-11-13 02:19:40 +0000 | [diff] [blame] | 1105 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1106 | |
Victor Stinner | d5c355c | 2011-04-30 14:53:09 +0200 | [diff] [blame] | 1107 | .. data:: thread_info |
| 1108 | |
| 1109 | A :term:`struct sequence` holding information about the thread |
| 1110 | implementation. |
| 1111 | |
| 1112 | +------------------+---------------------------------------------------------+ |
| 1113 | | Attribute | Explanation | |
| 1114 | +==================+=========================================================+ |
| 1115 | | :const:`name` | Name of the thread implementation: | |
| 1116 | | | | |
| 1117 | | | * ``'nt'``: Windows threads | |
Victor Stinner | d5c355c | 2011-04-30 14:53:09 +0200 | [diff] [blame] | 1118 | | | * ``'pthread'``: POSIX threads | |
| 1119 | | | * ``'solaris'``: Solaris threads | |
| 1120 | +------------------+---------------------------------------------------------+ |
| 1121 | | :const:`lock` | Name of the lock implementation: | |
| 1122 | | | | |
| 1123 | | | * ``'semaphore'``: a lock uses a semaphore | |
| 1124 | | | * ``'mutex+cond'``: a lock uses a mutex | |
| 1125 | | | and a condition variable | |
| 1126 | | | * ``None`` if this information is unknown | |
| 1127 | +------------------+---------------------------------------------------------+ |
| 1128 | | :const:`version` | Name and version of the thread library. It is a string, | |
| 1129 | | | or ``None`` if these informations are unknown. | |
| 1130 | +------------------+---------------------------------------------------------+ |
| 1131 | |
| 1132 | .. versionadded:: 3.3 |
| 1133 | |
| 1134 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1135 | .. data:: tracebacklimit |
| 1136 | |
| 1137 | When this variable is set to an integer value, it determines the maximum number |
| 1138 | of levels of traceback information printed when an unhandled exception occurs. |
| 1139 | The default is ``1000``. When set to ``0`` or less, all traceback information |
| 1140 | is suppressed and only the exception type and value are printed. |
| 1141 | |
| 1142 | |
| 1143 | .. data:: version |
| 1144 | |
| 1145 | A string containing the version number of the Python interpreter plus additional |
Georg Brandl | e42a59d | 2010-07-31 20:05:31 +0000 | [diff] [blame] | 1146 | information on the build number and compiler used. This string is displayed |
| 1147 | when the interactive interpreter is started. Do not extract version information |
| 1148 | out of it, rather, use :data:`version_info` and the functions provided by the |
| 1149 | :mod:`platform` module. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1150 | |
| 1151 | |
| 1152 | .. data:: api_version |
| 1153 | |
| 1154 | The C API version for this interpreter. Programmers may find this useful when |
| 1155 | debugging version conflicts between Python and extension modules. |
| 1156 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1157 | |
| 1158 | .. data:: version_info |
| 1159 | |
| 1160 | A tuple containing the five components of the version number: *major*, *minor*, |
| 1161 | *micro*, *releaselevel*, and *serial*. All values except *releaselevel* are |
| 1162 | integers; the release level is ``'alpha'``, ``'beta'``, ``'candidate'``, or |
| 1163 | ``'final'``. The ``version_info`` value corresponding to the Python version 2.0 |
Eric Smith | 0e5b562 | 2009-02-06 01:32:42 +0000 | [diff] [blame] | 1164 | is ``(2, 0, 0, 'final', 0)``. The components can also be accessed by name, |
| 1165 | so ``sys.version_info[0]`` is equivalent to ``sys.version_info.major`` |
| 1166 | and so on. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1167 | |
Raymond Hettinger | 35a8836 | 2009-04-09 00:08:24 +0000 | [diff] [blame] | 1168 | .. versionchanged:: 3.1 |
Georg Brandl | 67b21b7 | 2010-08-17 15:07:14 +0000 | [diff] [blame] | 1169 | Added named component attributes. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1170 | |
| 1171 | .. data:: warnoptions |
| 1172 | |
| 1173 | This is an implementation detail of the warnings framework; do not modify this |
| 1174 | value. Refer to the :mod:`warnings` module for more information on the warnings |
| 1175 | framework. |
| 1176 | |
| 1177 | |
| 1178 | .. data:: winver |
| 1179 | |
| 1180 | The version number used to form registry keys on Windows platforms. This is |
| 1181 | stored as string resource 1000 in the Python DLL. The value is normally the |
| 1182 | first three characters of :const:`version`. It is provided in the :mod:`sys` |
| 1183 | module for informational purposes; modifying this value has no effect on the |
| 1184 | registry keys used by Python. Availability: Windows. |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 1185 | |
Antoine Pitrou | 9583cac | 2010-10-21 13:42:28 +0000 | [diff] [blame] | 1186 | |
| 1187 | .. data:: _xoptions |
| 1188 | |
| 1189 | A dictionary of the various implementation-specific flags passed through |
| 1190 | the :option:`-X` command-line option. Option names are either mapped to |
| 1191 | their values, if given explicitly, or to :const:`True`. Example:: |
| 1192 | |
| 1193 | $ ./python -Xa=b -Xc |
| 1194 | Python 3.2a3+ (py3k, Oct 16 2010, 20:14:50) |
| 1195 | [GCC 4.4.3] on linux2 |
| 1196 | Type "help", "copyright", "credits" or "license" for more information. |
| 1197 | >>> import sys |
| 1198 | >>> sys._xoptions |
| 1199 | {'a': 'b', 'c': True} |
| 1200 | |
| 1201 | .. impl-detail:: |
| 1202 | |
| 1203 | This is a CPython-specific way of accessing options passed through |
| 1204 | :option:`-X`. Other implementations may export them through other |
| 1205 | means, or not at all. |
| 1206 | |
| 1207 | .. versionadded:: 3.2 |
| 1208 | |
| 1209 | |
Mark Dickinson | be5846b | 2010-07-02 20:26:07 +0000 | [diff] [blame] | 1210 | .. rubric:: Citations |
| 1211 | |
| 1212 | .. [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 . |
| 1213 | |