Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1 | |
| 2 | :mod:`sys` --- System-specific parameters and functions |
| 3 | ======================================================= |
| 4 | |
| 5 | .. module:: sys |
| 6 | :synopsis: Access system-specific parameters and functions. |
| 7 | |
| 8 | |
| 9 | This module provides access to some variables used or maintained by the |
| 10 | interpreter and to functions that interact strongly with the interpreter. It is |
| 11 | always available. |
| 12 | |
| 13 | |
| 14 | .. data:: argv |
| 15 | |
| 16 | The list of command line arguments passed to a Python script. ``argv[0]`` is the |
| 17 | script name (it is operating system dependent whether this is a full pathname or |
| 18 | not). If the command was executed using the :option:`-c` command line option to |
| 19 | the interpreter, ``argv[0]`` is set to the string ``'-c'``. If no script name |
| 20 | was passed to the Python interpreter, ``argv[0]`` is the empty string. |
| 21 | |
| 22 | To loop over the standard input, or the list of files given on the |
| 23 | command line, see the :mod:`fileinput` module. |
| 24 | |
| 25 | |
| 26 | .. data:: byteorder |
| 27 | |
| 28 | An indicator of the native byte order. This will have the value ``'big'`` on |
| 29 | big-endian (most-significant byte first) platforms, and ``'little'`` on |
| 30 | little-endian (least-significant byte first) platforms. |
| 31 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 32 | |
| 33 | .. data:: subversion |
| 34 | |
| 35 | A triple (repo, branch, version) representing the Subversion information of the |
| 36 | Python interpreter. *repo* is the name of the repository, ``'CPython'``. |
| 37 | *branch* is a string of one of the forms ``'trunk'``, ``'branches/name'`` or |
| 38 | ``'tags/name'``. *version* is the output of ``svnversion``, if the interpreter |
| 39 | was built from a Subversion checkout; it contains the revision number (range) |
| 40 | and possibly a trailing 'M' if there were local modifications. If the tree was |
| 41 | exported (or svnversion was not available), it is the revision of |
| 42 | ``Include/patchlevel.h`` if the branch is a tag. Otherwise, it is ``None``. |
| 43 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 44 | |
| 45 | .. data:: builtin_module_names |
| 46 | |
| 47 | A tuple of strings giving the names of all modules that are compiled into this |
| 48 | Python interpreter. (This information is not available in any other way --- |
| 49 | ``modules.keys()`` only lists the imported modules.) |
| 50 | |
| 51 | |
| 52 | .. data:: copyright |
| 53 | |
| 54 | A string containing the copyright pertaining to the Python interpreter. |
| 55 | |
| 56 | |
Christian Heimes | 15ebc88 | 2008-02-04 18:48:49 +0000 | [diff] [blame] | 57 | .. function:: _clear_type_cache() |
| 58 | |
| 59 | Clear the internal type cache. The type cache is used to speed up attribute |
| 60 | and method lookups. Use the function *only* to drop unnecessary references |
| 61 | during reference leak debugging. |
| 62 | |
| 63 | This function should be used for internal and specialized purposes only. |
Christian Heimes | 2685563 | 2008-01-27 23:50:43 +0000 | [diff] [blame] | 64 | |
Christian Heimes | 2685563 | 2008-01-27 23:50:43 +0000 | [diff] [blame] | 65 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 66 | .. function:: _current_frames() |
| 67 | |
| 68 | Return a dictionary mapping each thread's identifier to the topmost stack frame |
| 69 | currently active in that thread at the time the function is called. Note that |
| 70 | functions in the :mod:`traceback` module can build the call stack given such a |
| 71 | frame. |
| 72 | |
| 73 | This is most useful for debugging deadlock: this function does not require the |
| 74 | deadlocked threads' cooperation, and such threads' call stacks are frozen for as |
| 75 | long as they remain deadlocked. The frame returned for a non-deadlocked thread |
| 76 | may bear no relationship to that thread's current activity by the time calling |
| 77 | code examines the frame. |
| 78 | |
| 79 | This function should be used for internal and specialized purposes only. |
| 80 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 81 | |
| 82 | .. data:: dllhandle |
| 83 | |
| 84 | Integer specifying the handle of the Python DLL. Availability: Windows. |
| 85 | |
| 86 | |
| 87 | .. function:: displayhook(value) |
| 88 | |
| 89 | If *value* is not ``None``, this function prints it to ``sys.stdout``, and saves |
Georg Brandl | 1a3284e | 2007-12-02 09:40:06 +0000 | [diff] [blame] | 90 | it in ``builtins._``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 91 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 92 | ``sys.displayhook`` is called on the result of evaluating an :term:`expression` |
| 93 | entered in an interactive Python session. The display of these values can be |
| 94 | customized by assigning another one-argument function to ``sys.displayhook``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 95 | |
| 96 | |
| 97 | .. function:: excepthook(type, value, traceback) |
| 98 | |
| 99 | This function prints out a given traceback and exception to ``sys.stderr``. |
| 100 | |
| 101 | When an exception is raised and uncaught, the interpreter calls |
| 102 | ``sys.excepthook`` with three arguments, the exception class, exception |
| 103 | instance, and a traceback object. In an interactive session this happens just |
| 104 | before control is returned to the prompt; in a Python program this happens just |
| 105 | before the program exits. The handling of such top-level exceptions can be |
| 106 | customized by assigning another three-argument function to ``sys.excepthook``. |
| 107 | |
| 108 | |
| 109 | .. data:: __displayhook__ |
| 110 | __excepthook__ |
| 111 | |
| 112 | These objects contain the original values of ``displayhook`` and ``excepthook`` |
| 113 | at the start of the program. They are saved so that ``displayhook`` and |
| 114 | ``excepthook`` can be restored in case they happen to get replaced with broken |
| 115 | objects. |
| 116 | |
| 117 | |
| 118 | .. function:: exc_info() |
| 119 | |
| 120 | This function returns a tuple of three values that give information about the |
| 121 | exception that is currently being handled. The information returned is specific |
| 122 | both to the current thread and to the current stack frame. If the current stack |
| 123 | frame is not handling an exception, the information is taken from the calling |
| 124 | stack frame, or its caller, and so on until a stack frame is found that is |
| 125 | handling an exception. Here, "handling an exception" is defined as "executing |
Benjamin Peterson | eec3d71 | 2008-06-11 15:59:43 +0000 | [diff] [blame] | 126 | an except clause." For any stack frame, only information about the exception |
| 127 | being currently handled is accessible. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 128 | |
| 129 | .. index:: object: traceback |
| 130 | |
| 131 | If no exception is being handled anywhere on the stack, a tuple containing three |
| 132 | ``None`` values is returned. Otherwise, the values returned are ``(type, value, |
| 133 | traceback)``. Their meaning is: *type* gets the exception type of the exception |
| 134 | being handled (a class object); *value* gets the exception parameter (its |
| 135 | :dfn:`associated value` or the second argument to :keyword:`raise`, which is |
| 136 | always a class instance if the exception type is a class object); *traceback* |
| 137 | gets a traceback object (see the Reference Manual) which encapsulates the call |
| 138 | stack at the point where the exception originally occurred. |
| 139 | |
| 140 | .. warning:: |
| 141 | |
Georg Brandl | e6bcc91 | 2008-05-12 18:05:20 +0000 | [diff] [blame] | 142 | Assigning the *traceback* return value to a local variable in a function |
| 143 | that is handling an exception will cause a circular reference. Since most |
| 144 | functions don't need access to the traceback, the best solution is to use |
| 145 | something like ``exctype, value = sys.exc_info()[:2]`` to extract only the |
| 146 | exception type and value. If you do need the traceback, make sure to |
| 147 | delete it after use (best done with a :keyword:`try` |
| 148 | ... :keyword:`finally` statement) or to call :func:`exc_info` in a |
| 149 | function that does not itself handle an exception. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 150 | |
Georg Brandl | e6bcc91 | 2008-05-12 18:05:20 +0000 | [diff] [blame] | 151 | Such cycles are normally automatically reclaimed when garbage collection |
| 152 | is enabled and they become unreachable, but it remains more efficient to |
| 153 | avoid creating cycles. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 154 | |
| 155 | |
| 156 | .. data:: exec_prefix |
| 157 | |
| 158 | A string giving the site-specific directory prefix where the platform-dependent |
| 159 | Python files are installed; by default, this is also ``'/usr/local'``. This can |
| 160 | be set at build time with the :option:`--exec-prefix` argument to the |
| 161 | :program:`configure` script. Specifically, all configuration files (e.g. the |
| 162 | :file:`pyconfig.h` header file) are installed in the directory ``exec_prefix + |
| 163 | '/lib/pythonversion/config'``, and shared library modules are installed in |
| 164 | ``exec_prefix + '/lib/pythonversion/lib-dynload'``, where *version* is equal to |
| 165 | ``version[:3]``. |
| 166 | |
| 167 | |
| 168 | .. data:: executable |
| 169 | |
| 170 | A string giving the name of the executable binary for the Python interpreter, on |
| 171 | systems where this makes sense. |
| 172 | |
| 173 | |
| 174 | .. function:: exit([arg]) |
| 175 | |
| 176 | Exit from Python. This is implemented by raising the :exc:`SystemExit` |
| 177 | exception, so cleanup actions specified by finally clauses of :keyword:`try` |
| 178 | statements are honored, and it is possible to intercept the exit attempt at an |
| 179 | outer level. The optional argument *arg* can be an integer giving the exit |
| 180 | status (defaulting to zero), or another type of object. If it is an integer, |
| 181 | zero is considered "successful termination" and any nonzero value is considered |
| 182 | "abnormal termination" by shells and the like. Most systems require it to be in |
| 183 | the range 0-127, and produce undefined results otherwise. Some systems have a |
| 184 | convention for assigning specific meanings to specific exit codes, but these are |
| 185 | generally underdeveloped; Unix programs generally use 2 for command line syntax |
| 186 | errors and 1 for all other kind of errors. If another type of object is passed, |
| 187 | ``None`` is equivalent to passing zero, and any other object is printed to |
| 188 | ``sys.stderr`` and results in an exit code of 1. In particular, |
| 189 | ``sys.exit("some error message")`` is a quick way to exit a program when an |
| 190 | error occurs. |
| 191 | |
| 192 | |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 193 | .. data:: flags |
| 194 | |
| 195 | The struct sequence *flags* exposes the status of command line flags. The |
| 196 | attributes are read only. |
| 197 | |
| 198 | +------------------------------+------------------------------------------+ |
| 199 | | attribute | flag | |
| 200 | +==============================+==========================================+ |
| 201 | | :const:`debug` | -d | |
| 202 | +------------------------------+------------------------------------------+ |
| 203 | | :const:`py3k_warning` | -3 | |
| 204 | +------------------------------+------------------------------------------+ |
| 205 | | :const:`division_warning` | -Q | |
| 206 | +------------------------------+------------------------------------------+ |
| 207 | | :const:`division_new` | -Qnew | |
| 208 | +------------------------------+------------------------------------------+ |
| 209 | | :const:`inspect` | -i | |
| 210 | +------------------------------+------------------------------------------+ |
| 211 | | :const:`interactive` | -i | |
| 212 | +------------------------------+------------------------------------------+ |
| 213 | | :const:`optimize` | -O or -OO | |
| 214 | +------------------------------+------------------------------------------+ |
| 215 | | :const:`dont_write_bytecode` | -B | |
| 216 | +------------------------------+------------------------------------------+ |
| 217 | | :const:`no_site` | -S | |
| 218 | +------------------------------+------------------------------------------+ |
Guido van Rossum | 7736b5b | 2008-01-15 21:44:53 +0000 | [diff] [blame] | 219 | | :const:`ignore_environment` | -E | |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 220 | +------------------------------+------------------------------------------+ |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 221 | | :const:`verbose` | -v | |
| 222 | +------------------------------+------------------------------------------+ |
| 223 | | :const:`unicode` | -U | |
| 224 | +------------------------------+------------------------------------------+ |
| 225 | |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 226 | |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 227 | .. data:: float_info |
| 228 | |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 229 | A structseq holding information about the float type. It contains low level |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 230 | information about the precision and internal representation. Please study |
| 231 | your system's :file:`float.h` for more information. |
| 232 | |
| 233 | +---------------------+--------------------------------------------------+ |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 234 | | attribute | explanation | |
Christian Heimes | 9385266 | 2007-12-01 12:22:32 +0000 | [diff] [blame] | 235 | +=====================+==================================================+ |
| 236 | | :const:`epsilon` | Difference between 1 and the next representable | |
| 237 | | | floating point number | |
| 238 | +---------------------+--------------------------------------------------+ |
| 239 | | :const:`dig` | digits (see :file:`float.h`) | |
| 240 | +---------------------+--------------------------------------------------+ |
| 241 | | :const:`mant_dig` | mantissa digits (see :file:`float.h`) | |
| 242 | +---------------------+--------------------------------------------------+ |
| 243 | | :const:`max` | maximum representable finite float | |
| 244 | +---------------------+--------------------------------------------------+ |
| 245 | | :const:`max_exp` | maximum int e such that radix**(e-1) is in the | |
| 246 | | | range of finite representable floats | |
| 247 | +---------------------+--------------------------------------------------+ |
| 248 | | :const:`max_10_exp` | maximum int e such that 10**e is in the | |
| 249 | | | range of finite representable floats | |
| 250 | +---------------------+--------------------------------------------------+ |
| 251 | | :const:`min` | Minimum positive normalizer float | |
| 252 | +---------------------+--------------------------------------------------+ |
| 253 | | :const:`min_exp` | minimum int e such that radix**(e-1) is a | |
| 254 | | | normalized float | |
| 255 | +---------------------+--------------------------------------------------+ |
| 256 | | :const:`min_10_exp` | minimum int e such that 10**e is a normalized | |
| 257 | | | float | |
| 258 | +---------------------+--------------------------------------------------+ |
| 259 | | :const:`radix` | radix of exponent | |
| 260 | +---------------------+--------------------------------------------------+ |
| 261 | | :const:`rounds` | addition rounds (see :file:`float.h`) | |
| 262 | +---------------------+--------------------------------------------------+ |
| 263 | |
| 264 | .. note:: |
| 265 | |
| 266 | The information in the table is simplified. |
| 267 | |
| 268 | |
Mark Dickinson | b08a53a | 2009-04-16 19:52:09 +0000 | [diff] [blame] | 269 | .. data:: float_repr_style |
| 270 | |
| 271 | A string indicating how the :func:`repr` function behaves for |
| 272 | floats. If the string has value ``'short'`` then for a finite |
| 273 | float ``x``, ``repr(x)`` aims to produce a short string with the |
| 274 | property that ``float(repr(x)) == x``. This is the usual behaviour |
| 275 | in Python 3.1 and later. Otherwise, ``float_repr_style`` has value |
| 276 | ``'legacy'`` and ``repr(x)`` behaves in the same way as it did in |
| 277 | versions of Python prior to 3.1. |
| 278 | |
| 279 | .. versionadded:: 3.1 |
| 280 | |
| 281 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 282 | .. function:: getcheckinterval() |
| 283 | |
| 284 | Return the interpreter's "check interval"; see :func:`setcheckinterval`. |
| 285 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 286 | |
| 287 | .. function:: getdefaultencoding() |
| 288 | |
| 289 | Return the name of the current default string encoding used by the Unicode |
| 290 | implementation. |
| 291 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 292 | |
| 293 | .. function:: getdlopenflags() |
| 294 | |
| 295 | Return the current value of the flags that are used for :cfunc:`dlopen` calls. |
Neal Norwitz | 6cf49cf | 2008-03-24 06:22:57 +0000 | [diff] [blame] | 296 | 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] | 297 | Availability: Unix. |
| 298 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 299 | |
| 300 | .. function:: getfilesystemencoding() |
| 301 | |
| 302 | Return the name of the encoding used to convert Unicode filenames into system |
| 303 | file names, or ``None`` if the system default encoding is used. The result value |
| 304 | depends on the operating system: |
| 305 | |
| 306 | * On Windows 9x, the encoding is "mbcs". |
| 307 | |
| 308 | * On Mac OS X, the encoding is "utf-8". |
| 309 | |
| 310 | * On Unix, the encoding is the user's preference according to the result of |
| 311 | nl_langinfo(CODESET), or :const:`None` if the ``nl_langinfo(CODESET)`` failed. |
| 312 | |
| 313 | * On Windows NT+, file names are Unicode natively, so no conversion is |
| 314 | performed. :func:`getfilesystemencoding` still returns ``'mbcs'``, as this is |
| 315 | the encoding that applications should use when they explicitly want to convert |
| 316 | Unicode strings to byte strings that are equivalent when used as file names. |
| 317 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 318 | |
| 319 | .. function:: getrefcount(object) |
| 320 | |
| 321 | Return the reference count of the *object*. The count returned is generally one |
| 322 | higher than you might expect, because it includes the (temporary) reference as |
| 323 | an argument to :func:`getrefcount`. |
| 324 | |
| 325 | |
| 326 | .. function:: getrecursionlimit() |
| 327 | |
| 328 | Return the current value of the recursion limit, the maximum depth of the Python |
| 329 | interpreter stack. This limit prevents infinite recursion from causing an |
| 330 | overflow of the C stack and crashing Python. It can be set by |
| 331 | :func:`setrecursionlimit`. |
| 332 | |
| 333 | |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 334 | .. function:: getsizeof(object[, default]) |
Martin v. Löwis | 00709aa | 2008-06-04 14:18:43 +0000 | [diff] [blame] | 335 | |
| 336 | Return the size of an object in bytes. The object can be any type of |
| 337 | object. All built-in objects will return correct results, but this |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 338 | 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] | 339 | specific. |
| 340 | |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 341 | The *default* argument allows to define a value which will be returned |
| 342 | if the object type does not provide means to retrieve the size and would |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 343 | cause a `TypeError`. |
Robert Schuppenies | fbe94c5 | 2008-07-14 10:13:31 +0000 | [diff] [blame] | 344 | |
| 345 | func:`getsizeof` calls the object's __sizeof__ method and adds an additional |
| 346 | garbage collector overhead if the object is managed by the garbage collector. |
| 347 | |
Martin v. Löwis | 00709aa | 2008-06-04 14:18:43 +0000 | [diff] [blame] | 348 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 349 | .. function:: _getframe([depth]) |
| 350 | |
| 351 | Return a frame object from the call stack. If optional integer *depth* is |
| 352 | given, return the frame object that many calls below the top of the stack. If |
| 353 | that is deeper than the call stack, :exc:`ValueError` is raised. The default |
| 354 | for *depth* is zero, returning the frame at the top of the call stack. |
| 355 | |
| 356 | This function should be used for internal and specialized purposes only. |
| 357 | |
| 358 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 359 | .. function:: getprofile() |
| 360 | |
| 361 | .. index:: |
| 362 | single: profile function |
| 363 | single: profiler |
| 364 | |
| 365 | Get the profiler function as set by :func:`setprofile`. |
| 366 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 367 | |
| 368 | .. function:: gettrace() |
| 369 | |
| 370 | .. index:: |
| 371 | single: trace function |
| 372 | single: debugger |
| 373 | |
| 374 | Get the trace function as set by :func:`settrace`. |
| 375 | |
| 376 | .. note:: |
| 377 | |
| 378 | The :func:`gettrace` function is intended only for implementing debuggers, |
| 379 | profilers, coverage tools and the like. Its behavior is part of the |
| 380 | implementation platform, rather than part of the language definition, |
| 381 | and thus may not be available in all Python implementations. |
| 382 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 383 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 384 | .. function:: getwindowsversion() |
| 385 | |
| 386 | Return a tuple containing five components, describing the Windows version |
| 387 | currently running. The elements are *major*, *minor*, *build*, *platform*, and |
| 388 | *text*. *text* contains a string while all other values are integers. |
| 389 | |
| 390 | *platform* may be one of the following values: |
| 391 | |
Christian Heimes | 81ee3ef | 2008-05-04 22:42:01 +0000 | [diff] [blame] | 392 | +-----------------------------------------+-------------------------+ |
| 393 | | Constant | Platform | |
| 394 | +=========================================+=========================+ |
| 395 | | :const:`0 (VER_PLATFORM_WIN32s)` | Win32s on Windows 3.1 | |
| 396 | +-----------------------------------------+-------------------------+ |
| 397 | | :const:`1 (VER_PLATFORM_WIN32_WINDOWS)` | Windows 95/98/ME | |
| 398 | +-----------------------------------------+-------------------------+ |
| 399 | | :const:`2 (VER_PLATFORM_WIN32_NT)` | Windows NT/2000/XP/x64 | |
| 400 | +-----------------------------------------+-------------------------+ |
| 401 | | :const:`3 (VER_PLATFORM_WIN32_CE)` | Windows CE | |
| 402 | +-----------------------------------------+-------------------------+ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 403 | |
| 404 | This function wraps the Win32 :cfunc:`GetVersionEx` function; see the Microsoft |
| 405 | documentation for more information about these fields. |
| 406 | |
| 407 | Availability: Windows. |
| 408 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 409 | |
| 410 | .. data:: hexversion |
| 411 | |
| 412 | The version number encoded as a single integer. This is guaranteed to increase |
| 413 | with each version, including proper support for non-production releases. For |
| 414 | example, to test that the Python interpreter is at least version 1.5.2, use:: |
| 415 | |
| 416 | if sys.hexversion >= 0x010502F0: |
| 417 | # use some advanced feature |
| 418 | ... |
| 419 | else: |
| 420 | # use an alternative implementation or warn the user |
| 421 | ... |
| 422 | |
| 423 | This is called ``hexversion`` since it only really looks meaningful when viewed |
| 424 | as the result of passing it to the built-in :func:`hex` function. The |
| 425 | ``version_info`` value may be used for a more human-friendly encoding of the |
| 426 | same information. |
| 427 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 428 | |
Mark Dickinson | bd79264 | 2009-03-18 20:06:12 +0000 | [diff] [blame] | 429 | .. data:: int_info |
| 430 | |
| 431 | A struct sequence that holds information about Python's |
| 432 | internal representation of integers. The attributes are read only. |
| 433 | |
| 434 | +-------------------------+----------------------------------------------+ |
| 435 | | attribute | explanation | |
| 436 | +=========================+==============================================+ |
| 437 | | :const:`bits_per_digit` | number of bits held in each digit. Python | |
| 438 | | | integers are stored internally in base | |
| 439 | | | ``2**int_info.bits_per_digit`` | |
| 440 | +-------------------------+----------------------------------------------+ |
| 441 | | :const:`sizeof_digit` | size in bytes of the C type used to | |
| 442 | | | represent a digit | |
| 443 | +-------------------------+----------------------------------------------+ |
| 444 | |
Mark Dickinson | d72c7b6 | 2009-03-20 16:00:49 +0000 | [diff] [blame] | 445 | .. versionadded:: 3.1 |
| 446 | |
Mark Dickinson | bd79264 | 2009-03-18 20:06:12 +0000 | [diff] [blame] | 447 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 448 | .. function:: intern(string) |
| 449 | |
| 450 | Enter *string* in the table of "interned" strings and return the interned string |
| 451 | -- which is *string* itself or a copy. Interning strings is useful to gain a |
| 452 | little performance on dictionary lookup -- if the keys in a dictionary are |
| 453 | interned, and the lookup key is interned, the key comparisons (after hashing) |
| 454 | can be done by a pointer compare instead of a string compare. Normally, the |
| 455 | names used in Python programs are automatically interned, and the dictionaries |
| 456 | used to hold module, class or instance attributes have interned keys. |
| 457 | |
Georg Brandl | 55ac8f0 | 2007-09-01 13:51:09 +0000 | [diff] [blame] | 458 | Interned strings are not immortal; you must keep a reference to the return |
| 459 | value of :func:`intern` around to benefit from it. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 460 | |
| 461 | |
| 462 | .. data:: last_type |
| 463 | last_value |
| 464 | last_traceback |
| 465 | |
| 466 | These three variables are not always defined; they are set when an exception is |
| 467 | not handled and the interpreter prints an error message and a stack traceback. |
| 468 | Their intended use is to allow an interactive user to import a debugger module |
| 469 | and engage in post-mortem debugging without having to re-execute the command |
| 470 | that caused the error. (Typical use is ``import pdb; pdb.pm()`` to enter the |
| 471 | post-mortem debugger; see chapter :ref:`debugger` for |
| 472 | more information.) |
| 473 | |
| 474 | The meaning of the variables is the same as that of the return values from |
| 475 | :func:`exc_info` above. (Since there is only one interactive thread, |
| 476 | thread-safety is not a concern for these variables, unlike for ``exc_type`` |
| 477 | etc.) |
| 478 | |
| 479 | |
Christian Heimes | a37d4c6 | 2007-12-04 23:02:19 +0000 | [diff] [blame] | 480 | .. data:: maxsize |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 481 | |
Georg Brandl | 3377055 | 2007-12-15 09:55:35 +0000 | [diff] [blame] | 482 | An integer giving the maximum value a variable of type :ctype:`Py_ssize_t` can |
| 483 | take. It's usually ``2**31 - 1`` on a 32-bit platform and ``2**63 - 1`` on a |
| 484 | 64-bit platform. |
Christian Heimes | a37d4c6 | 2007-12-04 23:02:19 +0000 | [diff] [blame] | 485 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 486 | |
| 487 | .. data:: maxunicode |
| 488 | |
| 489 | An integer giving the largest supported code point for a Unicode character. The |
| 490 | value of this depends on the configuration option that specifies whether Unicode |
| 491 | characters are stored as UCS-2 or UCS-4. |
| 492 | |
| 493 | |
Brett Cannon | e43b060 | 2009-03-21 03:11:16 +0000 | [diff] [blame] | 494 | .. data:: meta_path |
| 495 | |
| 496 | A list of :term:`finder` objects that have their :meth:`find_module` |
| 497 | methods called to see if one of the objects can find the module to be |
| 498 | imported. The :meth:`find_module` method is called at least with the |
| 499 | absolute name of the module being imported. If the module to be imported is |
| 500 | contained in package then the parent package's :attr:`__path__` attribute |
| 501 | is passed in as a second argument. The method returns :keyword:`None` if |
| 502 | the module cannot be found, else returns a :term:`loader`. |
| 503 | |
| 504 | :data:`sys.meta_path` is searched before any implicit default finders or |
| 505 | :data:`sys.path`. |
| 506 | |
| 507 | See :pep:`302` for the original specification. |
| 508 | |
| 509 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 510 | .. data:: modules |
| 511 | |
| 512 | This is a dictionary that maps module names to modules which have already been |
| 513 | loaded. This can be manipulated to force reloading of modules and other tricks. |
| 514 | |
| 515 | |
| 516 | .. data:: path |
| 517 | |
| 518 | .. index:: triple: module; search; path |
| 519 | |
| 520 | A list of strings that specifies the search path for modules. Initialized from |
| 521 | the environment variable :envvar:`PYTHONPATH`, plus an installation-dependent |
| 522 | default. |
| 523 | |
| 524 | As initialized upon program startup, the first item of this list, ``path[0]``, |
| 525 | is the directory containing the script that was used to invoke the Python |
| 526 | interpreter. If the script directory is not available (e.g. if the interpreter |
| 527 | is invoked interactively or if the script is read from standard input), |
| 528 | ``path[0]`` is the empty string, which directs Python to search modules in the |
| 529 | current directory first. Notice that the script directory is inserted *before* |
| 530 | the entries inserted as a result of :envvar:`PYTHONPATH`. |
| 531 | |
| 532 | A program is free to modify this list for its own purposes. |
| 533 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 534 | |
Benjamin Peterson | 058e31e | 2009-01-16 03:54:08 +0000 | [diff] [blame] | 535 | .. seealso:: |
| 536 | Module :mod:`site` This describes how to use .pth files to extend |
| 537 | :data:`sys.path`. |
| 538 | |
| 539 | |
Brett Cannon | e43b060 | 2009-03-21 03:11:16 +0000 | [diff] [blame] | 540 | .. data:: path_hooks |
| 541 | |
| 542 | A list of callables that take a path argument to try to create a |
| 543 | :term:`finder` for the path. If a finder can be created, it is to be |
| 544 | returned by the callable, else raise :exc:`ImportError`. |
| 545 | |
| 546 | Originally specified in :pep:`302`. |
| 547 | |
| 548 | |
| 549 | .. data:: path_importer_cache |
| 550 | |
| 551 | A dictionary acting as a cache for :term:`finder` objects. The keys are |
| 552 | paths that have been passed to :data:`sys.path_hooks` and the values are |
| 553 | the finders that are found. If a path is a valid file system path but no |
| 554 | explicit finder is found on :data:`sys.path_hooks` then :keyword:`None` is |
| 555 | stored to represent the implicit default finder should be used. If the path |
| 556 | is not an existing path then :class:`imp.NullImporter` is set. |
| 557 | |
| 558 | Originally specified in :pep:`302`. |
| 559 | |
| 560 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 561 | .. data:: platform |
| 562 | |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 563 | This string contains a platform identifier that can be used to append |
| 564 | platform-specific components to :data:`sys.path`, for instance. |
| 565 | |
| 566 | For Unix systems, this is the lowercased OS name as returned by ``uname -s`` |
| 567 | with the first part of the version as returned by ``uname -r`` appended, |
| 568 | e.g. ``'sunos5'`` or ``'linux2'``, *at the time when Python was built*. |
| 569 | For other systems, the values are: |
| 570 | |
| 571 | ================ =========================== |
| 572 | System :data:`platform` value |
| 573 | ================ =========================== |
| 574 | Windows ``'win32'`` |
| 575 | Windows/Cygwin ``'cygwin'`` |
Georg Brandl | c575c90 | 2008-09-13 17:46:05 +0000 | [diff] [blame] | 576 | Mac OS X ``'darwin'`` |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 577 | OS/2 ``'os2'`` |
| 578 | OS/2 EMX ``'os2emx'`` |
Christian Heimes | 9bd667a | 2008-01-20 15:14:11 +0000 | [diff] [blame] | 579 | AtheOS ``'atheos'`` |
| 580 | ================ =========================== |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 581 | |
| 582 | |
| 583 | .. data:: prefix |
| 584 | |
| 585 | A string giving the site-specific directory prefix where the platform |
| 586 | independent Python files are installed; by default, this is the string |
| 587 | ``'/usr/local'``. This can be set at build time with the :option:`--prefix` |
| 588 | argument to the :program:`configure` script. The main collection of Python |
| 589 | library modules is installed in the directory ``prefix + '/lib/pythonversion'`` |
| 590 | while the platform independent header files (all except :file:`pyconfig.h`) are |
| 591 | stored in ``prefix + '/include/pythonversion'``, where *version* is equal to |
| 592 | ``version[:3]``. |
| 593 | |
| 594 | |
| 595 | .. data:: ps1 |
| 596 | ps2 |
| 597 | |
| 598 | .. index:: |
| 599 | single: interpreter prompts |
| 600 | single: prompts, interpreter |
| 601 | |
| 602 | Strings specifying the primary and secondary prompt of the interpreter. These |
| 603 | are only defined if the interpreter is in interactive mode. Their initial |
| 604 | values in this case are ``'>>> '`` and ``'... '``. If a non-string object is |
| 605 | assigned to either variable, its :func:`str` is re-evaluated each time the |
| 606 | interpreter prepares to read a new interactive command; this can be used to |
| 607 | implement a dynamic prompt. |
| 608 | |
| 609 | |
Christian Heimes | 790c823 | 2008-01-07 21:14:23 +0000 | [diff] [blame] | 610 | .. data:: dont_write_bytecode |
| 611 | |
| 612 | If this is true, Python won't try to write ``.pyc`` or ``.pyo`` files on the |
| 613 | import of source modules. This value is initially set to ``True`` or ``False`` |
| 614 | depending on the ``-B`` command line option and the ``PYTHONDONTWRITEBYTECODE`` |
| 615 | environment variable, but you can set it yourself to control bytecode file |
| 616 | generation. |
| 617 | |
Christian Heimes | 790c823 | 2008-01-07 21:14:23 +0000 | [diff] [blame] | 618 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 619 | .. function:: setcheckinterval(interval) |
| 620 | |
| 621 | Set the interpreter's "check interval". This integer value determines how often |
| 622 | the interpreter checks for periodic things such as thread switches and signal |
| 623 | handlers. The default is ``100``, meaning the check is performed every 100 |
| 624 | Python virtual instructions. Setting it to a larger value may increase |
| 625 | performance for programs using threads. Setting it to a value ``<=`` 0 checks |
| 626 | every virtual instruction, maximizing responsiveness as well as overhead. |
| 627 | |
| 628 | |
| 629 | .. function:: setdefaultencoding(name) |
| 630 | |
| 631 | Set the current default string encoding used by the Unicode implementation. If |
| 632 | *name* does not match any available encoding, :exc:`LookupError` is raised. |
| 633 | This function is only intended to be used by the :mod:`site` module |
| 634 | implementation and, where needed, by :mod:`sitecustomize`. Once used by the |
| 635 | :mod:`site` module, it is removed from the :mod:`sys` module's namespace. |
| 636 | |
Christian Heimes | 5b5e81c | 2007-12-31 16:14:33 +0000 | [diff] [blame] | 637 | .. Note that :mod:`site` is not imported if the :option:`-S` option is passed |
| 638 | to the interpreter, in which case this function will remain available. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 639 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 640 | |
| 641 | .. function:: setdlopenflags(n) |
| 642 | |
| 643 | Set the flags used by the interpreter for :cfunc:`dlopen` calls, such as when |
| 644 | the interpreter loads extension modules. Among other things, this will enable a |
| 645 | lazy resolving of symbols when importing a module, if called as |
| 646 | ``sys.setdlopenflags(0)``. To share symbols across extension modules, call as |
Neal Norwitz | 6cf49cf | 2008-03-24 06:22:57 +0000 | [diff] [blame] | 647 | ``sys.setdlopenflags(ctypes.RTLD_GLOBAL)``. Symbolic names for the |
| 648 | flag modules can be either found in the :mod:`ctypes` module, or in the :mod:`DLFCN` |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 649 | module. If :mod:`DLFCN` is not available, it can be generated from |
| 650 | :file:`/usr/include/dlfcn.h` using the :program:`h2py` script. Availability: |
| 651 | Unix. |
| 652 | |
Martin v. Löwis | 04dc25c | 2008-10-03 16:09:28 +0000 | [diff] [blame] | 653 | .. function:: setfilesystemencoding(enc) |
| 654 | |
| 655 | Set the encoding used when converting Python strings to file names to *enc*. |
| 656 | By default, Python tries to determine the encoding it should use automatically |
| 657 | on Unix; on Windows, it avoids such conversion completely. This function can |
| 658 | be used when Python's determination of the encoding needs to be overwritten, |
| 659 | e.g. when not all file names on disk can be decoded using the encoding that |
| 660 | Python had chosen. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 661 | |
| 662 | .. function:: setprofile(profilefunc) |
| 663 | |
| 664 | .. index:: |
| 665 | single: profile function |
| 666 | single: profiler |
| 667 | |
| 668 | Set the system's profile function, which allows you to implement a Python source |
| 669 | code profiler in Python. See chapter :ref:`profile` for more information on the |
| 670 | Python profiler. The system's profile function is called similarly to the |
| 671 | system's trace function (see :func:`settrace`), but it isn't called for each |
| 672 | executed line of code (only on call and return, but the return event is reported |
| 673 | even when an exception has been set). The function is thread-specific, but |
| 674 | there is no way for the profiler to know about context switches between threads, |
| 675 | so it does not make sense to use this in the presence of multiple threads. Also, |
| 676 | its return value is not used, so it can simply return ``None``. |
| 677 | |
| 678 | |
| 679 | .. function:: setrecursionlimit(limit) |
| 680 | |
| 681 | Set the maximum depth of the Python interpreter stack to *limit*. This limit |
| 682 | prevents infinite recursion from causing an overflow of the C stack and crashing |
| 683 | Python. |
| 684 | |
| 685 | The highest possible limit is platform-dependent. A user may need to set the |
| 686 | limit higher when she has a program that requires deep recursion and a platform |
| 687 | that supports a higher limit. This should be done with care, because a too-high |
| 688 | limit can lead to a crash. |
| 689 | |
| 690 | |
| 691 | .. function:: settrace(tracefunc) |
| 692 | |
| 693 | .. index:: |
| 694 | single: trace function |
| 695 | single: debugger |
| 696 | |
| 697 | 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] | 698 | source code debugger in Python. The function is thread-specific; for a |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 699 | debugger to support multiple threads, it must be registered using |
| 700 | :func:`settrace` for each thread being debugged. |
| 701 | |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 702 | Trace functions should have three arguments: *frame*, *event*, and |
| 703 | *arg*. *frame* is the current stack frame. *event* is a string: ``'call'``, |
| 704 | ``'line'``, ``'return'``, ``'exception'``, ``'c_call'``, ``'c_return'``, or |
| 705 | ``'c_exception'``. *arg* depends on the event type. |
| 706 | |
| 707 | The trace function is invoked (with *event* set to ``'call'``) whenever a new |
| 708 | local scope is entered; it should return a reference to a local trace |
| 709 | function to be used that scope, or ``None`` if the scope shouldn't be traced. |
| 710 | |
| 711 | The local trace function should return a reference to itself (or to another |
| 712 | function for further tracing in that scope), or ``None`` to turn off tracing |
| 713 | in that scope. |
| 714 | |
| 715 | The events have the following meaning: |
| 716 | |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 717 | ``'call'`` |
Amaury Forgeot d'Arc | b0c2916 | 2008-11-22 22:18:04 +0000 | [diff] [blame] | 718 | A function is called (or some other code block entered). The |
| 719 | global trace function is called; *arg* is ``None``; the return value |
| 720 | specifies the local trace function. |
| 721 | |
| 722 | ``'line'`` |
| 723 | The interpreter is about to execute a new line of code (sometimes multiple |
| 724 | line events on one line exist). The local trace function is called; *arg* |
| 725 | is ``None``; the return value specifies the new local trace function. |
| 726 | |
| 727 | ``'return'`` |
| 728 | A function (or other code block) is about to return. The local trace |
| 729 | function is called; *arg* is the value that will be returned. The trace |
| 730 | function's return value is ignored. |
| 731 | |
| 732 | ``'exception'`` |
| 733 | An exception has occurred. The local trace function is called; *arg* is a |
| 734 | tuple ``(exception, value, traceback)``; the return value specifies the |
| 735 | new local trace function. |
| 736 | |
| 737 | ``'c_call'`` |
| 738 | A C function is about to be called. This may be an extension function or |
| 739 | a builtin. *arg* is the C function object. |
| 740 | |
| 741 | ``'c_return'`` |
| 742 | A C function has returned. *arg* is ``None``. |
| 743 | |
| 744 | ``'c_exception'`` |
| 745 | A C function has thrown an exception. *arg* is ``None``. |
| 746 | |
| 747 | Note that as an exception is propagated down the chain of callers, an |
| 748 | ``'exception'`` event is generated at each level. |
| 749 | |
| 750 | For more information on code and frame objects, refer to :ref:`types`. |
| 751 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 752 | .. note:: |
| 753 | |
| 754 | The :func:`settrace` function is intended only for implementing debuggers, |
| 755 | profilers, coverage tools and the like. Its behavior is part of the |
| 756 | implementation platform, rather than part of the language definition, and thus |
| 757 | may not be available in all Python implementations. |
| 758 | |
| 759 | |
| 760 | .. function:: settscdump(on_flag) |
| 761 | |
| 762 | Activate dumping of VM measurements using the Pentium timestamp counter, if |
| 763 | *on_flag* is true. Deactivate these dumps if *on_flag* is off. The function is |
| 764 | available only if Python was compiled with :option:`--with-tsc`. To understand |
| 765 | the output of this dump, read :file:`Python/ceval.c` in the Python sources. |
| 766 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 767 | |
| 768 | .. data:: stdin |
| 769 | stdout |
| 770 | stderr |
| 771 | |
| 772 | File objects corresponding to the interpreter's standard input, output and error |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 773 | streams. ``stdin`` is used for all interpreter input except for scripts but |
| 774 | including calls to :func:`input`. ``stdout`` is used for |
| 775 | the output of :func:`print` and :term:`expression` statements and for the |
| 776 | prompts of :func:`input`. The interpreter's own prompts |
| 777 | and (almost all of) its error messages go to ``stderr``. ``stdout`` and |
| 778 | ``stderr`` needn't be built-in file objects: any object is acceptable as long |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 779 | as it has a :meth:`write` method that takes a string argument. (Changing these |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 780 | objects doesn't affect the standard I/O streams of processes executed by |
| 781 | :func:`os.popen`, :func:`os.system` or the :func:`exec\*` family of functions in |
| 782 | the :mod:`os` module.) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 783 | |
Benjamin Peterson | 3261fa5 | 2009-05-12 03:01:51 +0000 | [diff] [blame] | 784 | The standard streams are in text mode by default. To write or read binary |
| 785 | data to these, use the underlying binary buffer. For example, to write bytes |
| 786 | to :data:`stdout`, use ``sys.stdout.buffer.write(b'abc')``. Using |
Benjamin Peterson | 12f29ff | 2009-05-12 20:58:26 +0000 | [diff] [blame] | 787 | :meth:`io.TextIOBase.detach` streams can be made binary by default. For |
| 788 | example, this function sets all the standard streams to binary:: |
Benjamin Peterson | 4199d60 | 2009-05-12 20:47:57 +0000 | [diff] [blame] | 789 | |
| 790 | def make_streams_binary(): |
| 791 | sys.stdin = sys.stdin.detach() |
Benjamin Peterson | 4487f53 | 2009-05-13 21:15:03 +0000 | [diff] [blame] | 792 | sys.stdout = sys.stdout.detach() |
Benjamin Peterson | 4199d60 | 2009-05-12 20:47:57 +0000 | [diff] [blame] | 793 | sys.stderr = sys.stderr.detach() |
Benjamin Peterson | eb9fc52 | 2008-12-07 14:58:03 +0000 | [diff] [blame] | 794 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 795 | |
| 796 | .. data:: __stdin__ |
| 797 | __stdout__ |
| 798 | __stderr__ |
| 799 | |
| 800 | These objects contain the original values of ``stdin``, ``stderr`` and |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 801 | ``stdout`` at the start of the program. They are used during finalization, |
| 802 | and could be useful to print to the actual standard stream no matter if the |
| 803 | ``sys.std*`` object has been redirected. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 804 | |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 805 | It can also be used to restore the actual files to known working file objects |
| 806 | in case they have been overwritten with a broken object. However, the |
| 807 | preferred way to do this is to explicitly save the previous stream before |
| 808 | replacing it, and restore the saved object. |
Christian Heimes | 58cb1b8 | 2007-11-13 02:19:40 +0000 | [diff] [blame] | 809 | |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 810 | .. note:: |
| 811 | Under some conditions ``stdin``, ``stdout`` and ``stderr`` as well as the |
| 812 | original values ``__stdin__``, ``__stdout__`` and ``__stderr__`` can be |
| 813 | None. It is usually the case for Windows GUI apps that aren't connected |
| 814 | to a console and Python apps started with :program:`pythonw`. |
Christian Heimes | 58cb1b8 | 2007-11-13 02:19:40 +0000 | [diff] [blame] | 815 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 816 | |
| 817 | .. data:: tracebacklimit |
| 818 | |
| 819 | When this variable is set to an integer value, it determines the maximum number |
| 820 | of levels of traceback information printed when an unhandled exception occurs. |
| 821 | The default is ``1000``. When set to ``0`` or less, all traceback information |
| 822 | is suppressed and only the exception type and value are printed. |
| 823 | |
| 824 | |
| 825 | .. data:: version |
| 826 | |
| 827 | A string containing the version number of the Python interpreter plus additional |
| 828 | information on the build number and compiler used. It has a value of the form |
| 829 | ``'version (#build_number, build_date, build_time) [compiler]'``. The first |
| 830 | three characters are used to identify the version in the installation |
| 831 | directories (where appropriate on each platform). An example:: |
| 832 | |
| 833 | >>> import sys |
| 834 | >>> sys.version |
| 835 | '1.5.2 (#0 Apr 13 1999, 10:51:12) [MSC 32 bit (Intel)]' |
| 836 | |
| 837 | |
| 838 | .. data:: api_version |
| 839 | |
| 840 | The C API version for this interpreter. Programmers may find this useful when |
| 841 | debugging version conflicts between Python and extension modules. |
| 842 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 843 | |
| 844 | .. data:: version_info |
| 845 | |
| 846 | A tuple containing the five components of the version number: *major*, *minor*, |
| 847 | *micro*, *releaselevel*, and *serial*. All values except *releaselevel* are |
| 848 | integers; the release level is ``'alpha'``, ``'beta'``, ``'candidate'``, or |
| 849 | ``'final'``. The ``version_info`` value corresponding to the Python version 2.0 |
Eric Smith | 0e5b562 | 2009-02-06 01:32:42 +0000 | [diff] [blame] | 850 | is ``(2, 0, 0, 'final', 0)``. The components can also be accessed by name, |
| 851 | so ``sys.version_info[0]`` is equivalent to ``sys.version_info.major`` |
| 852 | and so on. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 853 | |
Raymond Hettinger | 35a8836 | 2009-04-09 00:08:24 +0000 | [diff] [blame] | 854 | .. versionchanged:: 3.1 |
Eric Smith | 0e5b562 | 2009-02-06 01:32:42 +0000 | [diff] [blame] | 855 | Added named component attributes |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 856 | |
| 857 | .. data:: warnoptions |
| 858 | |
| 859 | This is an implementation detail of the warnings framework; do not modify this |
| 860 | value. Refer to the :mod:`warnings` module for more information on the warnings |
| 861 | framework. |
| 862 | |
| 863 | |
| 864 | .. data:: winver |
| 865 | |
| 866 | The version number used to form registry keys on Windows platforms. This is |
| 867 | stored as string resource 1000 in the Python DLL. The value is normally the |
| 868 | first three characters of :const:`version`. It is provided in the :mod:`sys` |
| 869 | module for informational purposes; modifying this value has no effect on the |
| 870 | registry keys used by Python. Availability: Windows. |