Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame^] | 1 | |
| 2 | :mod:`inspect` --- Inspect live objects |
| 3 | ======================================= |
| 4 | |
| 5 | .. module:: inspect |
| 6 | :synopsis: Extract information and source code from live objects. |
| 7 | .. moduleauthor:: Ka-Ping Yee <ping@lfw.org> |
| 8 | .. sectionauthor:: Ka-Ping Yee <ping@lfw.org> |
| 9 | |
| 10 | |
| 11 | .. versionadded:: 2.1 |
| 12 | |
| 13 | The :mod:`inspect` module provides several useful functions to help get |
| 14 | information about live objects such as modules, classes, methods, functions, |
| 15 | tracebacks, frame objects, and code objects. For example, it can help you |
| 16 | examine the contents of a class, retrieve the source code of a method, extract |
| 17 | and format the argument list for a function, or get all the information you need |
| 18 | to display a detailed traceback. |
| 19 | |
| 20 | There are four main kinds of services provided by this module: type checking, |
| 21 | getting source code, inspecting classes and functions, and examining the |
| 22 | interpreter stack. |
| 23 | |
| 24 | |
| 25 | .. _inspect-types: |
| 26 | |
| 27 | Types and members |
| 28 | ----------------- |
| 29 | |
| 30 | The :func:`getmembers` function retrieves the members of an object such as a |
| 31 | class or module. The eleven functions whose names begin with "is" are mainly |
| 32 | provided as convenient choices for the second argument to :func:`getmembers`. |
| 33 | They also help you determine when you can expect to find the following special |
| 34 | attributes: |
| 35 | |
| 36 | +-----------+-----------------+---------------------------+-------+ |
| 37 | | Type | Attribute | Description | Notes | |
| 38 | +===========+=================+===========================+=======+ |
| 39 | | module | __doc__ | documentation string | | |
| 40 | +-----------+-----------------+---------------------------+-------+ |
| 41 | | | __file__ | filename (missing for | | |
| 42 | | | | built-in modules) | | |
| 43 | +-----------+-----------------+---------------------------+-------+ |
| 44 | | class | __doc__ | documentation string | | |
| 45 | +-----------+-----------------+---------------------------+-------+ |
| 46 | | | __module__ | name of module in which | | |
| 47 | | | | this class was defined | | |
| 48 | +-----------+-----------------+---------------------------+-------+ |
| 49 | | method | __doc__ | documentation string | | |
| 50 | +-----------+-----------------+---------------------------+-------+ |
| 51 | | | __name__ | name with which this | | |
| 52 | | | | method was defined | | |
| 53 | +-----------+-----------------+---------------------------+-------+ |
| 54 | | | im_class | class object that asked | \(1) | |
| 55 | | | | for this method | | |
| 56 | +-----------+-----------------+---------------------------+-------+ |
| 57 | | | im_func | function object | | |
| 58 | | | | containing implementation | | |
| 59 | | | | of method | | |
| 60 | +-----------+-----------------+---------------------------+-------+ |
| 61 | | | im_self | instance to which this | | |
| 62 | | | | method is bound, or | | |
| 63 | | | | ``None`` | | |
| 64 | +-----------+-----------------+---------------------------+-------+ |
| 65 | | function | __doc__ | documentation string | | |
| 66 | +-----------+-----------------+---------------------------+-------+ |
| 67 | | | __name__ | name with which this | | |
| 68 | | | | function was defined | | |
| 69 | +-----------+-----------------+---------------------------+-------+ |
| 70 | | | __code__ | code object containing | | |
| 71 | | | | compiled function | | |
| 72 | | | | bytecode | | |
| 73 | +-----------+-----------------+---------------------------+-------+ |
| 74 | | | __defaults__ | tuple of any default | | |
| 75 | | | | values for arguments | | |
| 76 | +-----------+-----------------+---------------------------+-------+ |
| 77 | | | __globals__ | global namespace in which | | |
| 78 | | | | this function was defined | | |
| 79 | +-----------+-----------------+---------------------------+-------+ |
| 80 | | traceback | tb_frame | frame object at this | | |
| 81 | | | | level | | |
| 82 | +-----------+-----------------+---------------------------+-------+ |
| 83 | | | tb_lasti | index of last attempted | | |
| 84 | | | | instruction in bytecode | | |
| 85 | +-----------+-----------------+---------------------------+-------+ |
| 86 | | | tb_lineno | current line number in | | |
| 87 | | | | Python source code | | |
| 88 | +-----------+-----------------+---------------------------+-------+ |
| 89 | | | tb_next | next inner traceback | | |
| 90 | | | | object (called by this | | |
| 91 | | | | level) | | |
| 92 | +-----------+-----------------+---------------------------+-------+ |
| 93 | | frame | f_back | next outer frame object | | |
| 94 | | | | (this frame's caller) | | |
| 95 | +-----------+-----------------+---------------------------+-------+ |
| 96 | | | f_builtins | built-in namespace seen | | |
| 97 | | | | by this frame | | |
| 98 | +-----------+-----------------+---------------------------+-------+ |
| 99 | | | f_code | code object being | | |
| 100 | | | | executed in this frame | | |
| 101 | +-----------+-----------------+---------------------------+-------+ |
| 102 | | | f_exc_traceback | traceback if raised in | | |
| 103 | | | | this frame, or ``None`` | | |
| 104 | +-----------+-----------------+---------------------------+-------+ |
| 105 | | | f_exc_type | exception type if raised | | |
| 106 | | | | in this frame, or | | |
| 107 | | | | ``None`` | | |
| 108 | +-----------+-----------------+---------------------------+-------+ |
| 109 | | | f_exc_value | exception value if raised | | |
| 110 | | | | in this frame, or | | |
| 111 | | | | ``None`` | | |
| 112 | +-----------+-----------------+---------------------------+-------+ |
| 113 | | | f_globals | global namespace seen by | | |
| 114 | | | | this frame | | |
| 115 | +-----------+-----------------+---------------------------+-------+ |
| 116 | | | f_lasti | index of last attempted | | |
| 117 | | | | instruction in bytecode | | |
| 118 | +-----------+-----------------+---------------------------+-------+ |
| 119 | | | f_lineno | current line number in | | |
| 120 | | | | Python source code | | |
| 121 | +-----------+-----------------+---------------------------+-------+ |
| 122 | | | f_locals | local namespace seen by | | |
| 123 | | | | this frame | | |
| 124 | +-----------+-----------------+---------------------------+-------+ |
| 125 | | | f_restricted | 0 or 1 if frame is in | | |
| 126 | | | | restricted execution mode | | |
| 127 | +-----------+-----------------+---------------------------+-------+ |
| 128 | | | f_trace | tracing function for this | | |
| 129 | | | | frame, or ``None`` | | |
| 130 | +-----------+-----------------+---------------------------+-------+ |
| 131 | | code | co_argcount | number of arguments (not | | |
| 132 | | | | including \* or \*\* | | |
| 133 | | | | args) | | |
| 134 | +-----------+-----------------+---------------------------+-------+ |
| 135 | | | co_code | string of raw compiled | | |
| 136 | | | | bytecode | | |
| 137 | +-----------+-----------------+---------------------------+-------+ |
| 138 | | | co_consts | tuple of constants used | | |
| 139 | | | | in the bytecode | | |
| 140 | +-----------+-----------------+---------------------------+-------+ |
| 141 | | | co_filename | name of file in which | | |
| 142 | | | | this code object was | | |
| 143 | | | | created | | |
| 144 | +-----------+-----------------+---------------------------+-------+ |
| 145 | | | co_firstlineno | number of first line in | | |
| 146 | | | | Python source code | | |
| 147 | +-----------+-----------------+---------------------------+-------+ |
| 148 | | | co_flags | bitmap: 1=optimized ``|`` | | |
| 149 | | | | 2=newlocals ``|`` 4=\*arg | | |
| 150 | | | | ``|`` 8=\*\*arg | | |
| 151 | +-----------+-----------------+---------------------------+-------+ |
| 152 | | | co_lnotab | encoded mapping of line | | |
| 153 | | | | numbers to bytecode | | |
| 154 | | | | indices | | |
| 155 | +-----------+-----------------+---------------------------+-------+ |
| 156 | | | co_name | name with which this code | | |
| 157 | | | | object was defined | | |
| 158 | +-----------+-----------------+---------------------------+-------+ |
| 159 | | | co_names | tuple of names of local | | |
| 160 | | | | variables | | |
| 161 | +-----------+-----------------+---------------------------+-------+ |
| 162 | | | co_nlocals | number of local variables | | |
| 163 | +-----------+-----------------+---------------------------+-------+ |
| 164 | | | co_stacksize | virtual machine stack | | |
| 165 | | | | space required | | |
| 166 | +-----------+-----------------+---------------------------+-------+ |
| 167 | | | co_varnames | tuple of names of | | |
| 168 | | | | arguments and local | | |
| 169 | | | | variables | | |
| 170 | +-----------+-----------------+---------------------------+-------+ |
| 171 | | builtin | __doc__ | documentation string | | |
| 172 | +-----------+-----------------+---------------------------+-------+ |
| 173 | | | __name__ | original name of this | | |
| 174 | | | | function or method | | |
| 175 | +-----------+-----------------+---------------------------+-------+ |
| 176 | | | __self__ | instance to which a | | |
| 177 | | | | method is bound, or | | |
| 178 | | | | ``None`` | | |
| 179 | +-----------+-----------------+---------------------------+-------+ |
| 180 | |
| 181 | Note: |
| 182 | |
| 183 | (1) |
| 184 | .. versionchanged:: 2.2 |
| 185 | :attr:`im_class` used to refer to the class that defined the method. |
| 186 | |
| 187 | |
| 188 | .. function:: getmembers(object[, predicate]) |
| 189 | |
| 190 | Return all the members of an object in a list of (name, value) pairs sorted by |
| 191 | name. If the optional *predicate* argument is supplied, only members for which |
| 192 | the predicate returns a true value are included. |
| 193 | |
| 194 | |
| 195 | .. function:: getmoduleinfo(path) |
| 196 | |
| 197 | Return a tuple of values that describe how Python will interpret the file |
| 198 | identified by *path* if it is a module, or ``None`` if it would not be |
| 199 | identified as a module. The return tuple is ``(name, suffix, mode, mtype)``, |
| 200 | where *name* is the name of the module without the name of any enclosing |
| 201 | package, *suffix* is the trailing part of the file name (which may not be a |
| 202 | dot-delimited extension), *mode* is the :func:`open` mode that would be used |
| 203 | (``'r'`` or ``'rb'``), and *mtype* is an integer giving the type of the |
| 204 | module. *mtype* will have a value which can be compared to the constants |
| 205 | defined in the :mod:`imp` module; see the documentation for that module for |
| 206 | more information on module types. |
| 207 | |
| 208 | |
| 209 | .. function:: getmodulename(path) |
| 210 | |
| 211 | Return the name of the module named by the file *path*, without including the |
| 212 | names of enclosing packages. This uses the same algorithm as the interpreter |
| 213 | uses when searching for modules. If the name cannot be matched according to the |
| 214 | interpreter's rules, ``None`` is returned. |
| 215 | |
| 216 | |
| 217 | .. function:: ismodule(object) |
| 218 | |
| 219 | Return true if the object is a module. |
| 220 | |
| 221 | |
| 222 | .. function:: isclass(object) |
| 223 | |
| 224 | Return true if the object is a class. |
| 225 | |
| 226 | |
| 227 | .. function:: ismethod(object) |
| 228 | |
| 229 | Return true if the object is a method. |
| 230 | |
| 231 | |
| 232 | .. function:: isfunction(object) |
| 233 | |
| 234 | Return true if the object is a Python function or unnamed (lambda) function. |
| 235 | |
| 236 | |
| 237 | .. function:: istraceback(object) |
| 238 | |
| 239 | Return true if the object is a traceback. |
| 240 | |
| 241 | |
| 242 | .. function:: isframe(object) |
| 243 | |
| 244 | Return true if the object is a frame. |
| 245 | |
| 246 | |
| 247 | .. function:: iscode(object) |
| 248 | |
| 249 | Return true if the object is a code. |
| 250 | |
| 251 | |
| 252 | .. function:: isbuiltin(object) |
| 253 | |
| 254 | Return true if the object is a built-in function. |
| 255 | |
| 256 | |
| 257 | .. function:: isroutine(object) |
| 258 | |
| 259 | Return true if the object is a user-defined or built-in function or method. |
| 260 | |
| 261 | |
| 262 | .. function:: ismethoddescriptor(object) |
| 263 | |
| 264 | Return true if the object is a method descriptor, but not if ismethod() or |
| 265 | isclass() or isfunction() are true. |
| 266 | |
| 267 | This is new as of Python 2.2, and, for example, is true of int.__add__. An |
| 268 | object passing this test has a __get__ attribute but not a __set__ attribute, |
| 269 | but beyond that the set of attributes varies. __name__ is usually sensible, and |
| 270 | __doc__ often is. |
| 271 | |
| 272 | Methods implemented via descriptors that also pass one of the other tests return |
| 273 | false from the ismethoddescriptor() test, simply because the other tests promise |
| 274 | more -- you can, e.g., count on having the im_func attribute (etc) when an |
| 275 | object passes ismethod(). |
| 276 | |
| 277 | |
| 278 | .. function:: isdatadescriptor(object) |
| 279 | |
| 280 | Return true if the object is a data descriptor. |
| 281 | |
| 282 | Data descriptors have both a __get__ and a __set__ attribute. Examples are |
| 283 | properties (defined in Python), getsets, and members. The latter two are |
| 284 | defined in C and there are more specific tests available for those types, which |
| 285 | is robust across Python implementations. Typically, data descriptors will also |
| 286 | have __name__ and __doc__ attributes (properties, getsets, and members have both |
| 287 | of these attributes), but this is not guaranteed. |
| 288 | |
| 289 | .. versionadded:: 2.3 |
| 290 | |
| 291 | |
| 292 | .. function:: isgetsetdescriptor(object) |
| 293 | |
| 294 | Return true if the object is a getset descriptor. |
| 295 | |
| 296 | getsets are attributes defined in extension modules via ``PyGetSetDef`` |
| 297 | structures. For Python implementations without such types, this method will |
| 298 | always return ``False``. |
| 299 | |
| 300 | .. versionadded:: 2.5 |
| 301 | |
| 302 | |
| 303 | .. function:: ismemberdescriptor(object) |
| 304 | |
| 305 | Return true if the object is a member descriptor. |
| 306 | |
| 307 | Member descriptors are attributes defined in extension modules via |
| 308 | ``PyMemberDef`` structures. For Python implementations without such types, this |
| 309 | method will always return ``False``. |
| 310 | |
| 311 | .. versionadded:: 2.5 |
| 312 | |
| 313 | |
| 314 | .. _inspect-source: |
| 315 | |
| 316 | Retrieving source code |
| 317 | ---------------------- |
| 318 | |
| 319 | |
| 320 | .. function:: getdoc(object) |
| 321 | |
| 322 | Get the documentation string for an object. All tabs are expanded to spaces. To |
| 323 | clean up docstrings that are indented to line up with blocks of code, any |
| 324 | whitespace than can be uniformly removed from the second line onwards is |
| 325 | removed. |
| 326 | |
| 327 | |
| 328 | .. function:: getcomments(object) |
| 329 | |
| 330 | Return in a single string any lines of comments immediately preceding the |
| 331 | object's source code (for a class, function, or method), or at the top of the |
| 332 | Python source file (if the object is a module). |
| 333 | |
| 334 | |
| 335 | .. function:: getfile(object) |
| 336 | |
| 337 | Return the name of the (text or binary) file in which an object was defined. |
| 338 | This will fail with a :exc:`TypeError` if the object is a built-in module, |
| 339 | class, or function. |
| 340 | |
| 341 | |
| 342 | .. function:: getmodule(object) |
| 343 | |
| 344 | Try to guess which module an object was defined in. |
| 345 | |
| 346 | |
| 347 | .. function:: getsourcefile(object) |
| 348 | |
| 349 | Return the name of the Python source file in which an object was defined. This |
| 350 | will fail with a :exc:`TypeError` if the object is a built-in module, class, or |
| 351 | function. |
| 352 | |
| 353 | |
| 354 | .. function:: getsourcelines(object) |
| 355 | |
| 356 | Return a list of source lines and starting line number for an object. The |
| 357 | argument may be a module, class, method, function, traceback, frame, or code |
| 358 | object. The source code is returned as a list of the lines corresponding to the |
| 359 | object and the line number indicates where in the original source file the first |
| 360 | line of code was found. An :exc:`IOError` is raised if the source code cannot |
| 361 | be retrieved. |
| 362 | |
| 363 | |
| 364 | .. function:: getsource(object) |
| 365 | |
| 366 | Return the text of the source code for an object. The argument may be a module, |
| 367 | class, method, function, traceback, frame, or code object. The source code is |
| 368 | returned as a single string. An :exc:`IOError` is raised if the source code |
| 369 | cannot be retrieved. |
| 370 | |
| 371 | |
| 372 | .. _inspect-classes-functions: |
| 373 | |
| 374 | Classes and functions |
| 375 | --------------------- |
| 376 | |
| 377 | |
| 378 | .. function:: getclasstree(classes[, unique]) |
| 379 | |
| 380 | Arrange the given list of classes into a hierarchy of nested lists. Where a |
| 381 | nested list appears, it contains classes derived from the class whose entry |
| 382 | immediately precedes the list. Each entry is a 2-tuple containing a class and a |
| 383 | tuple of its base classes. If the *unique* argument is true, exactly one entry |
| 384 | appears in the returned structure for each class in the given list. Otherwise, |
| 385 | classes using multiple inheritance and their descendants will appear multiple |
| 386 | times. |
| 387 | |
| 388 | |
| 389 | .. function:: getargspec(func) |
| 390 | |
| 391 | Get the names and default values of a function's arguments. A tuple of four |
| 392 | things is returned: ``(args, varargs, varkw, defaults)``. *args* is a list of |
| 393 | the argument names (it may contain nested lists). *varargs* and *varkw* are the |
| 394 | names of the ``*`` and ``**`` arguments or ``None``. *defaults* is a tuple of |
| 395 | default argument values or None if there are no default arguments; if this tuple |
| 396 | has *n* elements, they correspond to the last *n* elements listed in *args*. |
| 397 | |
| 398 | |
| 399 | .. function:: getargvalues(frame) |
| 400 | |
| 401 | Get information about arguments passed into a particular frame. A tuple of four |
| 402 | things is returned: ``(args, varargs, varkw, locals)``. *args* is a list of the |
| 403 | argument names (it may contain nested lists). *varargs* and *varkw* are the |
| 404 | names of the ``*`` and ``**`` arguments or ``None``. *locals* is the locals |
| 405 | dictionary of the given frame. |
| 406 | |
| 407 | |
| 408 | .. function:: formatargspec(args[, varargs, varkw, defaults, formatarg, formatvarargs, formatvarkw, formatvalue, join]) |
| 409 | |
| 410 | Format a pretty argument spec from the four values returned by |
| 411 | :func:`getargspec`. The format\* arguments are the corresponding optional |
| 412 | formatting functions that are called to turn names and values into strings. |
| 413 | |
| 414 | |
| 415 | .. function:: formatargvalues(args[, varargs, varkw, locals, formatarg, formatvarargs, formatvarkw, formatvalue, join]) |
| 416 | |
| 417 | Format a pretty argument spec from the four values returned by |
| 418 | :func:`getargvalues`. The format\* arguments are the corresponding optional |
| 419 | formatting functions that are called to turn names and values into strings. |
| 420 | |
| 421 | |
| 422 | .. function:: getmro(cls) |
| 423 | |
| 424 | Return a tuple of class cls's base classes, including cls, in method resolution |
| 425 | order. No class appears more than once in this tuple. Note that the method |
| 426 | resolution order depends on cls's type. Unless a very peculiar user-defined |
| 427 | metatype is in use, cls will be the first element of the tuple. |
| 428 | |
| 429 | |
| 430 | .. _inspect-stack: |
| 431 | |
| 432 | The interpreter stack |
| 433 | --------------------- |
| 434 | |
| 435 | When the following functions return "frame records," each record is a tuple of |
| 436 | six items: the frame object, the filename, the line number of the current line, |
| 437 | the function name, a list of lines of context from the source code, and the |
| 438 | index of the current line within that list. |
| 439 | |
| 440 | .. warning:: |
| 441 | |
| 442 | Keeping references to frame objects, as found in the first element of the frame |
| 443 | records these functions return, can cause your program to create reference |
| 444 | cycles. Once a reference cycle has been created, the lifespan of all objects |
| 445 | which can be accessed from the objects which form the cycle can become much |
| 446 | longer even if Python's optional cycle detector is enabled. If such cycles must |
| 447 | be created, it is important to ensure they are explicitly broken to avoid the |
| 448 | delayed destruction of objects and increased memory consumption which occurs. |
| 449 | |
| 450 | Though the cycle detector will catch these, destruction of the frames (and local |
| 451 | variables) can be made deterministic by removing the cycle in a |
| 452 | :keyword:`finally` clause. This is also important if the cycle detector was |
| 453 | disabled when Python was compiled or using :func:`gc.disable`. For example:: |
| 454 | |
| 455 | def handle_stackframe_without_leak(): |
| 456 | frame = inspect.currentframe() |
| 457 | try: |
| 458 | # do something with the frame |
| 459 | finally: |
| 460 | del frame |
| 461 | |
| 462 | The optional *context* argument supported by most of these functions specifies |
| 463 | the number of lines of context to return, which are centered around the current |
| 464 | line. |
| 465 | |
| 466 | |
| 467 | .. function:: getframeinfo(frame[, context]) |
| 468 | |
| 469 | Get information about a frame or traceback object. A 5-tuple is returned, the |
| 470 | last five elements of the frame's frame record. |
| 471 | |
| 472 | |
| 473 | .. function:: getouterframes(frame[, context]) |
| 474 | |
| 475 | Get a list of frame records for a frame and all outer frames. These frames |
| 476 | represent the calls that lead to the creation of *frame*. The first entry in the |
| 477 | returned list represents *frame*; the last entry represents the outermost call |
| 478 | on *frame*'s stack. |
| 479 | |
| 480 | |
| 481 | .. function:: getinnerframes(traceback[, context]) |
| 482 | |
| 483 | Get a list of frame records for a traceback's frame and all inner frames. These |
| 484 | frames represent calls made as a consequence of *frame*. The first entry in the |
| 485 | list represents *traceback*; the last entry represents where the exception was |
| 486 | raised. |
| 487 | |
| 488 | |
| 489 | .. function:: currentframe() |
| 490 | |
| 491 | Return the frame object for the caller's stack frame. |
| 492 | |
| 493 | |
| 494 | .. function:: stack([context]) |
| 495 | |
| 496 | Return a list of frame records for the caller's stack. The first entry in the |
| 497 | returned list represents the caller; the last entry represents the outermost |
| 498 | call on the stack. |
| 499 | |
| 500 | |
| 501 | .. function:: trace([context]) |
| 502 | |
| 503 | Return a list of frame records for the stack between the current frame and the |
| 504 | frame in which an exception currently being handled was raised in. The first |
| 505 | entry in the list represents the caller; the last entry represents where the |
| 506 | exception was raised. |
| 507 | |