Lib/inspect.py

   1 """Get useful information from live Python objects.
   2
   3 This module encapsulates the interface provided by the internal special
   4 attributes (func_*, co_*, im_*, tb_*, etc.) in a friendlier fashion.
   5 It also provides some help for examining source code and class layout.
   6
   7 Here are some of the useful functions provided by this module:
   8
   9     ismodule(), isclass(), ismethod(), isfunction(), istraceback(),
  10         isframe(), iscode(), isbuiltin(), isroutine() - check object types
  11     getmembers() - get members of an object that satisfy a given condition
  12
  13     getfile(), getsourcefile(), getsource() - find an object's source code
  14     getdoc(), getcomments() - get documentation on an object
  15     getmodule() - determine the module that an object came from
  16     getclasstree() - arrange classes so as to represent their hierarchy
  17
  18     getargspec(), getargvalues() - get info about function arguments
  19     formatargspec(), formatargvalues() - format an argument spec
  20     getouterframes(), getinnerframes() - get info about frames
  21     currentframe() - get the current stack frame
  22     stack(), trace() - get info about frames on the stack or in a traceback
  23 """
  24
  25 # This module is in the public domain.  No warranties.
  26
  27 __author__ = 'Ka-Ping Yee <ping@lfw.org>'
  28 __date__ = '1 Jan 2001'
  29
  30 import sys, os, types, string, re, dis, imp, tokenize
  31
  32 # ----------------------------------------------------------- type-checking
  33 def ismodule(object):
  34     """Return true if the object is a module.
  35
  36     Module objects provide these attributes:
  37         __doc__         documentation string
  38         __file__        filename (missing for built-in modules)"""
  39     return isinstance(object, types.ModuleType)
  40
  41 def isclass(object):
  42     """Return true if the object is a class.
  43
  44     Class objects provide these attributes:
  45         __doc__         documentation string
  46         __module__      name of module in which this class was defined"""
  47     return isinstance(object, types.ClassType) or hasattr(object, '__bases__')
  48
  49 def ismethod(object):
  50     """Return true if the object is an instance method.
  51
  52     Instance method objects provide these attributes:
  53         __doc__         documentation string
  54         __name__        name with which this method was defined
  55         im_class        class object in which this method belongs
  56         im_func         function object containing implementation of method
  57         im_self         instance to which this method is bound, or None"""
  58     return isinstance(object, types.MethodType)
  59
  60 def ismethoddescriptor(object):
  61     """Return true if the object is a method descriptor.
  62
  63     But not if ismethod() or isclass() or isfunction() are true.
  64
  65     This is new in Python 2.2, and, for example, is true of int.__add__.
  66     An object passing this test has a __get__ attribute but not a __set__
  67     attribute, but beyond that the set of attributes varies.  __name__ is
  68     usually sensible, and __doc__ often is.
  69
  70     Methods implemented via descriptors that also pass one of the other
  71     tests return false from the ismethoddescriptor() test, simply because
  72     the other tests promise more -- you can, e.g., count on having the
  73     im_func attribute (etc) when an object passes ismethod()."""
  74     return (hasattr(object, "__get__")
  75             and not hasattr(object, "__set__") # else it's a data descriptor
  76             and not ismethod(object)           # mutual exclusion
  77             and not isfunction(object)
  78             and not isclass(object))
  79
  80 def isfunction(object):
  81     """Return true if the object is a user-defined function.
  82
  83     Function objects provide these attributes:
  84         __doc__         documentation string
  85         __name__        name with which this function was defined
  86         func_code       code object containing compiled function bytecode
  87         func_defaults   tuple of any default values for arguments
  88         func_doc        (same as __doc__)
  89         func_globals    global namespace in which this function was defined
  90         func_name       (same as __name__)"""
  91     return isinstance(object, types.FunctionType)
  92
  93 def istraceback(object):
  94     """Return true if the object is a traceback.
  95
  96     Traceback objects provide these attributes:
  97         tb_frame        frame object at this level
  98         tb_lasti        index of last attempted instruction in bytecode
  99         tb_lineno       current line number in Python source code
 100         tb_next         next inner traceback object (called by this level)"""
 101     return isinstance(object, types.TracebackType)
 102
 103 def isframe(object):
 104     """Return true if the object is a frame object.
 105
 106     Frame objects provide these attributes:
 107         f_back          next outer frame object (this frame's caller)
 108         f_builtins      built-in namespace seen by this frame
 109         f_code          code object being executed in this frame
 110         f_exc_traceback traceback if raised in this frame, or None
 111         f_exc_type      exception type if raised in this frame, or None
 112         f_exc_value     exception value if raised in this frame, or None
 113         f_globals       global namespace seen by this frame
 114         f_lasti         index of last attempted instruction in bytecode
 115         f_lineno        current line number in Python source code
 116         f_locals        local namespace seen by this frame
 117         f_restricted    0 or 1 if frame is in restricted execution mode
 118         f_trace         tracing function for this frame, or None"""
 119     return isinstance(object, types.FrameType)
 120
 121 def iscode(object):
 122     """Return true if the object is a code object.
 123
 124     Code objects provide these attributes:
 125         co_argcount     number of arguments (not including * or ** args)
 126         co_code         string of raw compiled bytecode
 127         co_consts       tuple of constants used in the bytecode
 128         co_filename     name of file in which this code object was created
 129         co_firstlineno  number of first line in Python source code
 130         co_flags        bitmap: 1=optimized | 2=newlocals | 4=*arg | 8=**arg
 131         co_lnotab       encoded mapping of line numbers to bytecode indices
 132         co_name         name with which this code object was defined
 133         co_names        tuple of names of local variables
 134         co_nlocals      number of local variables
 135         co_stacksize    virtual machine stack space required
 136         co_varnames     tuple of names of arguments and local variables"""
 137     return isinstance(object, types.CodeType)
 138
 139 def isbuiltin(object):
 140     """Return true if the object is a built-in function or method.
 141
 142     Built-in functions and methods provide these attributes:
 143         __doc__         documentation string
 144         __name__        original name of this function or method
 145         __self__        instance to which a method is bound, or None"""
 146     return isinstance(object, types.BuiltinFunctionType)
 147
 148 def isroutine(object):
 149     """Return true if the object is any kind of function or method."""
 150     return (isbuiltin(object)
 151             or isfunction(object)
 152             or ismethod(object)
 153             or ismethoddescriptor(object))
 154
 155 def getmembers(object, predicate=None):
 156     """Return all members of an object as (name, value) pairs sorted by name.
 157     Optionally, only return members that satisfy a given predicate."""
 158     results = []
 159     for key in dir(object):
 160         value = getattr(object, key)
 161         if not predicate or predicate(value):
 162             results.append((key, value))
 163     results.sort()
 164     return results
 165
 166 def classify_class_attrs(cls):
 167     """Return list of attribute-descriptor tuples.
 168
 169     For each name in dir(cls), the return list contains a 4-tuple
 170     with these elements:
 171
 172         0. The name (a string).
 173
 174         1. The kind of attribute this is, one of these strings:
 175                'class method'    created via classmethod()
 176                'static method'   created via staticmethod()
 177                'property'        created via property()
 178                'method'          any other flavor of method
 179                'data'            not a method
 180
 181         2. The class which defined this attribute (a class).
 182
 183         3. The object as obtained directly from the defining class's
 184            __dict__, not via getattr.  This is especially important for
 185            data attributes:  C.data is just a data object, but
 186            C.__dict__['data'] may be a data descriptor with additional
 187            info, like a __doc__ string.
 188     """
 189
 190     mro = getmro(cls)
 191     names = dir(cls)
 192     result = []
 193     for name in names:
 194         # Get the object associated with the name.
 195         # Getting an obj from the __dict__ sometimes reveals more than
 196         # using getattr.  Static and class methods are dramatic examples.
 197         if name in cls.__dict__:
 198             obj = cls.__dict__[name]
 199         else:
 200             obj = getattr(cls, name)
 201
 202         # Figure out where it was defined.
 203         homecls = getattr(obj, "__objclass__", None)
 204         if homecls is None:
 205             # search the dicts.
 206             for base in mro:
 207                 if name in base.__dict__:
 208                     homecls = base
 209                     break
 210
 211         # Get the object again, in order to get it from the defining
 212         # __dict__ instead of via getattr (if possible).
 213         if homecls is not None and name in homecls.__dict__:
 214             obj = homecls.__dict__[name]
 215
 216         # Also get the object via getattr.
 217         obj_via_getattr = getattr(cls, name)
 218
 219         # Classify the object.
 220         if isinstance(obj, staticmethod):
 221             kind = "static method"
 222         elif isinstance(obj, classmethod):
 223             kind = "class method"
 224         elif isinstance(obj, property):
 225             kind = "property"
 226         elif (ismethod(obj_via_getattr) or
 227               ismethoddescriptor(obj_via_getattr)):
 228             kind = "method"
 229         else:
 230             kind = "data"
 231
 232         result.append((name, kind, homecls, obj))
 233
 234     return result
 235
 236 # ----------------------------------------------------------- class helpers
 237 def _searchbases(cls, accum):
 238     # Simulate the "classic class" search order.
 239     if cls in accum:
 240         return
 241     accum.append(cls)
 242     for base in cls.__bases__:
 243         _searchbases(base, accum)
 244
 245 def getmro(cls):
 246     "Return tuple of base classes (including cls) in method resolution order."
 247     if hasattr(cls, "__mro__"):
 248         return cls.__mro__
 249     else:
 250         result = []
 251         _searchbases(cls, result)
 252         return tuple(result)
 253
 254 # -------------------------------------------------- source code extraction
 255 def indentsize(line):
 256     """Return the indent size, in spaces, at the start of a line of text."""
 257     expline = string.expandtabs(line)
 258     return len(expline) - len(string.lstrip(expline))
 259
 260 def getdoc(object):
 261     """Get the documentation string for an object.
 262
 263     All tabs are expanded to spaces.  To clean up docstrings that are
 264     indented to line up with blocks of code, any whitespace than can be
 265     uniformly removed from the second line onwards is removed."""
 266     try:
 267         doc = object.__doc__
 268     except AttributeError:
 269         return None
 270     if not isinstance(doc, (str, unicode)):
 271         return None
 272     try:
 273         lines = string.split(string.expandtabs(doc), '\n')
 274     except UnicodeError:
 275         return None
 276     else:
 277         margin = None
 278         for line in lines[1:]:
 279             content = len(string.lstrip(line))
 280             if not content: continue
 281             indent = len(line) - content
 282             if margin is None: margin = indent
 283             else: margin = min(margin, indent)
 284         if margin is not None:
 285             for i in range(1, len(lines)): lines[i] = lines[i][margin:]
 286         return string.join(lines, '\n')
 287
 288 def getfile(object):
 289     """Work out which source or compiled file an object was defined in."""
 290     if ismodule(object):
 291         if hasattr(object, '__file__'):
 292             return object.__file__
 293         raise TypeError, 'arg is a built-in module'
 294     if isclass(object):
 295         object = sys.modules.get(object.__module__)
 296         if hasattr(object, '__file__'):
 297             return object.__file__
 298         raise TypeError, 'arg is a built-in class'
 299     if ismethod(object):
 300         object = object.im_func
 301     if isfunction(object):
 302         object = object.func_code
 303     if istraceback(object):
 304         object = object.tb_frame
 305     if isframe(object):
 306         object = object.f_code
 307     if iscode(object):
 308         return object.co_filename
 309     raise TypeError, 'arg is not a module, class, method, ' \
 310                      'function, traceback, frame, or code object'
 311
 312 def getmoduleinfo(path):
 313     """Get the module name, suffix, mode, and module type for a given file."""
 314     filename = os.path.basename(path)
 315     suffixes = map(lambda (suffix, mode, mtype):
 316                    (-len(suffix), suffix, mode, mtype), imp.get_suffixes())
 317     suffixes.sort() # try longest suffixes first, in case they overlap
 318     for neglen, suffix, mode, mtype in suffixes:
 319         if filename[neglen:] == suffix:
 320             return filename[:neglen], suffix, mode, mtype
 321
 322 def getmodulename(path):
 323     """Return the module name for a given file, or None."""
 324     info = getmoduleinfo(path)
 325     if info: return info[0]
 326
 327 def getsourcefile(object):
 328     """Return the Python source file an object was defined in, if it exists."""
 329     filename = getfile(object)
 330     if string.lower(filename[-4:]) in ['.pyc', '.pyo']:
 331         filename = filename[:-4] + '.py'
 332     for suffix, mode, kind in imp.get_suffixes():
 333         if 'b' in mode and string.lower(filename[-len(suffix):]) == suffix:
 334             # Looks like a binary file.  We want to only return a text file.
 335             return None
 336     if os.path.exists(filename):
 337         return filename
 338
 339 def getabsfile(object):
 340     """Return an absolute path to the source or compiled file for an object.
 341
 342     The idea is for each object to have a unique origin, so this routine
 343     normalizes the result as much as possible."""
 344     return os.path.normcase(
 345         os.path.abspath(getsourcefile(object) or getfile(object)))
 346
 347 modulesbyfile = {}
 348
 349 def getmodule(object):
 350     """Return the module an object was defined in, or None if not found."""
 351     if ismodule(object):
 352         return object
 353     if isclass(object):
 354         return sys.modules.get(object.__module__)
 355     try:
 356         file = getabsfile(object)
 357     except TypeError:
 358         return None
 359     if modulesbyfile.has_key(file):
 360         return sys.modules[modulesbyfile[file]]
 361     for module in sys.modules.values():
 362         if hasattr(module, '__file__'):
 363             modulesbyfile[getabsfile(module)] = module.__name__
 364     if modulesbyfile.has_key(file):
 365         return sys.modules[modulesbyfile[file]]
 366     main = sys.modules['__main__']
 367     if hasattr(main, object.__name__):
 368         mainobject = getattr(main, object.__name__)
 369         if mainobject is object:
 370             return main
 371     builtin = sys.modules['__builtin__']
 372     if hasattr(builtin, object.__name__):
 373         builtinobject = getattr(builtin, object.__name__)
 374         if builtinobject is object:
 375             return builtin
 376
 377 def findsource(object):
 378     """Return the entire source file and starting line number for an object.
 379
 380     The argument may be a module, class, method, function, traceback, frame,
 381     or code object.  The source code is returned as a list of all the lines
 382     in the file and the line number indexes a line in that list.  An IOError
 383     is raised if the source code cannot be retrieved."""
 384     try:
 385         file = open(getsourcefile(object))
 386     except (TypeError, IOError):
 387         raise IOError, 'could not get source code'
 388     lines = file.readlines()
 389     file.close()
 390
 391     if ismodule(object):
 392         return lines, 0
 393
 394     if isclass(object):
 395         name = object.__name__
 396         pat = re.compile(r'^\s*class\s*' + name + r'\b')
 397         for i in range(len(lines)):
 398             if pat.match(lines[i]): return lines, i
 399         else: raise IOError, 'could not find class definition'
 400
 401     if ismethod(object):
 402         object = object.im_func
 403     if isfunction(object):
 404         object = object.func_code
 405     if istraceback(object):
 406         object = object.tb_frame
 407     if isframe(object):
 408         object = object.f_code
 409     if iscode(object):
 410         if not hasattr(object, 'co_firstlineno'):
 411             raise IOError, 'could not find function definition'
 412         lnum = object.co_firstlineno - 1
 413         pat = re.compile(r'^\s*def\s')
 414         while lnum > 0:
 415             if pat.match(lines[lnum]): break
 416             lnum = lnum - 1
 417         return lines, lnum
 418     raise IOError, 'could not find code object'
 419
 420 def getcomments(object):
 421     """Get lines of comments immediately preceding an object's source code."""
 422     try: lines, lnum = findsource(object)
 423     except IOError: return None
 424
 425     if ismodule(object):
 426         # Look for a comment block at the top of the file.
 427         start = 0
 428         if lines and lines[0][:2] == '#!': start = 1
 429         while start < len(lines) and string.strip(lines[start]) in ['', '#']:
 430             start = start + 1
 431         if start < len(lines) and lines[start][:1] == '#':
 432             comments = []
 433             end = start
 434             while end < len(lines) and lines[end][:1] == '#':
 435                 comments.append(string.expandtabs(lines[end]))
 436                 end = end + 1
 437             return string.join(comments, '')
 438
 439     # Look for a preceding block of comments at the same indentation.
 440     elif lnum > 0:
 441         indent = indentsize(lines[lnum])
 442         end = lnum - 1
 443         if end >= 0 and string.lstrip(lines[end])[:1] == '#' and \
 444             indentsize(lines[end]) == indent:
 445             comments = [string.lstrip(string.expandtabs(lines[end]))]
 446             if end > 0:
 447                 end = end - 1
 448                 comment = string.lstrip(string.expandtabs(lines[end]))
 449                 while comment[:1] == '#' and indentsize(lines[end]) == indent:
 450                     comments[:0] = [comment]
 451                     end = end - 1
 452                     if end < 0: break
 453                     comment = string.lstrip(string.expandtabs(lines[end]))
 454             while comments and string.strip(comments[0]) == '#':
 455                 comments[:1] = []
 456             while comments and string.strip(comments[-1]) == '#':
 457                 comments[-1:] = []
 458             return string.join(comments, '')
 459
 460 class ListReader:
 461     """Provide a readline() method to return lines from a list of strings."""
 462     def __init__(self, lines):
 463         self.lines = lines
 464         self.index = 0
 465
 466     def readline(self):
 467         i = self.index
 468         if i < len(self.lines):
 469             self.index = i + 1
 470             return self.lines[i]
 471         else: return ''
 472
 473 class EndOfBlock(Exception): pass
 474
 475 class BlockFinder:
 476     """Provide a tokeneater() method to detect the end of a code block."""
 477     def __init__(self):
 478         self.indent = 0
 479         self.started = 0
 480         self.last = 0
 481
 482     def tokeneater(self, type, token, (srow, scol), (erow, ecol), line):
 483         if not self.started:
 484             if type == tokenize.NAME: self.started = 1
 485         elif type == tokenize.NEWLINE:
 486             self.last = srow
 487         elif type == tokenize.INDENT:
 488             self.indent = self.indent + 1
 489         elif type == tokenize.DEDENT:
 490             self.indent = self.indent - 1
 491             if self.indent == 0: raise EndOfBlock, self.last
 492
 493 def getblock(lines):
 494     """Extract the block of code at the top of the given list of lines."""
 495     try:
 496         tokenize.tokenize(ListReader(lines).readline, BlockFinder().tokeneater)
 497     except EndOfBlock, eob:
 498         return lines[:eob.args[0]]
 499
 500 def getsourcelines(object):
 501     """Return a list of source lines and starting line number for an object.
 502
 503     The argument may be a module, class, method, function, traceback, frame,
 504     or code object.  The source code is returned as a list of the lines
 505     corresponding to the object and the line number indicates where in the
 506     original source file the first line of code was found.  An IOError is
 507     raised if the source code cannot be retrieved."""
 508     lines, lnum = findsource(object)
 509
 510     if ismodule(object): return lines, 0
 511     else: return getblock(lines[lnum:]), lnum + 1
 512
 513 def getsource(object):
 514     """Return the text of the source code for an object.
 515
 516     The argument may be a module, class, method, function, traceback, frame,
 517     or code object.  The source code is returned as a single string.  An
 518     IOError is raised if the source code cannot be retrieved."""
 519     lines, lnum = getsourcelines(object)
 520     return string.join(lines, '')
 521
 522 # --------------------------------------------------- class tree extraction
 523 def walktree(classes, children, parent):
 524     """Recursive helper function for getclasstree()."""
 525     results = []
 526     classes.sort(lambda a, b: cmp(a.__name__, b.__name__))
 527     for c in classes:
 528         results.append((c, c.__bases__))
 529         if children.has_key(c):
 530             results.append(walktree(children[c], children, c))
 531     return results
 532
 533 def getclasstree(classes, unique=0):
 534     """Arrange the given list of classes into a hierarchy of nested lists.
 535
 536     Where a nested list appears, it contains classes derived from the class
 537     whose entry immediately precedes the list.  Each entry is a 2-tuple
 538     containing a class and a tuple of its base classes.  If the 'unique'
 539     argument is true, exactly one entry appears in the returned structure
 540     for each class in the given list.  Otherwise, classes using multiple
 541     inheritance and their descendants will appear multiple times."""
 542     children = {}
 543     roots = []
 544     for c in classes:
 545         if c.__bases__:
 546             for parent in c.__bases__:
 547                 if not children.has_key(parent):
 548                     children[parent] = []
 549                 children[parent].append(c)
 550                 if unique and parent in classes: break
 551         elif c not in roots:
 552             roots.append(c)
 553     for parent in children.keys():
 554         if parent not in classes:
 555             roots.append(parent)
 556     return walktree(roots, children, None)
 557
 558 # ------------------------------------------------ argument list extraction
 559 # These constants are from Python's compile.h.
 560 CO_OPTIMIZED, CO_NEWLOCALS, CO_VARARGS, CO_VARKEYWORDS = 1, 2, 4, 8
 561
 562 def getargs(co):
 563     """Get information about the arguments accepted by a code object.
 564
 565     Three things are returned: (args, varargs, varkw), where 'args' is
 566     a list of argument names (possibly containing nested lists), and
 567     'varargs' and 'varkw' are the names of the * and ** arguments or None."""
 568     if not iscode(co): raise TypeError, 'arg is not a code object'
 569
 570     code = co.co_code
 571     nargs = co.co_argcount
 572     names = co.co_varnames
 573     args = list(names[:nargs])
 574     step = 0
 575
 576     # The following acrobatics are for anonymous (tuple) arguments.
 577     for i in range(nargs):
 578         if args[i][:1] in ['', '.']:
 579             stack, remain, count = [], [], []
 580             while step < len(code):
 581                 op = ord(code[step])
 582                 step = step + 1
 583                 if op >= dis.HAVE_ARGUMENT:
 584                     opname = dis.opname[op]
 585                     value = ord(code[step]) + ord(code[step+1])*256
 586                     step = step + 2
 587                     if opname in ['UNPACK_TUPLE', 'UNPACK_SEQUENCE']:
 588                         remain.append(value)
 589                         count.append(value)
 590                     elif opname == 'STORE_FAST':
 591                         stack.append(names[value])
 592                         remain[-1] = remain[-1] - 1
 593                         while remain[-1] == 0:
 594                             remain.pop()
 595                             size = count.pop()
 596                             stack[-size:] = [stack[-size:]]
 597                             if not remain: break
 598                             remain[-1] = remain[-1] - 1
 599                         if not remain: break
 600             args[i] = stack[0]
 601
 602     varargs = None
 603     if co.co_flags & CO_VARARGS:
 604         varargs = co.co_varnames[nargs]
 605         nargs = nargs + 1
 606     varkw = None
 607     if co.co_flags & CO_VARKEYWORDS:
 608         varkw = co.co_varnames[nargs]
 609     return args, varargs, varkw
 610
 611 def getargspec(func):
 612     """Get the names and default values of a function's arguments.
 613
 614     A tuple of four things is returned: (args, varargs, varkw, defaults).
 615     'args' is a list of the argument names (it may contain nested lists).
 616     'varargs' and 'varkw' are the names of the * and ** arguments or None.
 617     'defaults' is an n-tuple of the default values of the last n arguments."""
 618     if not isfunction(func): raise TypeError, 'arg is not a Python function'
 619     args, varargs, varkw = getargs(func.func_code)
 620     return args, varargs, varkw, func.func_defaults
 621
 622 def getargvalues(frame):
 623     """Get information about arguments passed into a particular frame.
 624
 625     A tuple of four things is returned: (args, varargs, varkw, locals).
 626     'args' is a list of the argument names (it may contain nested lists).
 627     'varargs' and 'varkw' are the names of the * and ** arguments or None.
 628     'locals' is the locals dictionary of the given frame."""
 629     args, varargs, varkw = getargs(frame.f_code)
 630     return args, varargs, varkw, frame.f_locals
 631
 632 def joinseq(seq):
 633     if len(seq) == 1:
 634         return '(' + seq[0] + ',)'
 635     else:
 636         return '(' + string.join(seq, ', ') + ')'
 637
 638 def strseq(object, convert, join=joinseq):
 639     """Recursively walk a sequence, stringifying each element."""
 640     if type(object) in [types.ListType, types.TupleType]:
 641         return join(map(lambda o, c=convert, j=join: strseq(o, c, j), object))
 642     else:
 643         return convert(object)
 644
 645 def formatargspec(args, varargs=None, varkw=None, defaults=None,
 646                   formatarg=str,
 647                   formatvarargs=lambda name: '*' + name,
 648                   formatvarkw=lambda name: '**' + name,
 649                   formatvalue=lambda value: '=' + repr(value),
 650                   join=joinseq):
 651     """Format an argument spec from the 4 values returned by getargspec.
 652
 653     The first four arguments are (args, varargs, varkw, defaults).  The
 654     other four arguments are the corresponding optional formatting functions
 655     that are called to turn names and values into strings.  The ninth
 656     argument is an optional function to format the sequence of arguments."""
 657     specs = []
 658     if defaults:
 659         firstdefault = len(args) - len(defaults)
 660     for i in range(len(args)):
 661         spec = strseq(args[i], formatarg, join)
 662         if defaults and i >= firstdefault:
 663             spec = spec + formatvalue(defaults[i - firstdefault])
 664         specs.append(spec)
 665     if varargs:
 666         specs.append(formatvarargs(varargs))
 667     if varkw:
 668         specs.append(formatvarkw(varkw))
 669     return '(' + string.join(specs, ', ') + ')'
 670
 671 def formatargvalues(args, varargs, varkw, locals,
 672                     formatarg=str,
 673                     formatvarargs=lambda name: '*' + name,
 674                     formatvarkw=lambda name: '**' + name,
 675                     formatvalue=lambda value: '=' + repr(value),
 676                     join=joinseq):
 677     """Format an argument spec from the 4 values returned by getargvalues.
 678
 679     The first four arguments are (args, varargs, varkw, locals).  The
 680     next four arguments are the corresponding optional formatting functions
 681     that are called to turn names and values into strings.  The ninth
 682     argument is an optional function to format the sequence of arguments."""
 683     def convert(name, locals=locals,
 684                 formatarg=formatarg, formatvalue=formatvalue):
 685         return formatarg(name) + formatvalue(locals[name])
 686     specs = []
 687     for i in range(len(args)):
 688         specs.append(strseq(args[i], convert, join))
 689     if varargs:
 690         specs.append(formatvarargs(varargs) + formatvalue(locals[varargs]))
 691     if varkw:
 692         specs.append(formatvarkw(varkw) + formatvalue(locals[varkw]))
 693     return '(' + string.join(specs, ', ') + ')'
 694
 695 # -------------------------------------------------- stack frame extraction
 696 def getframeinfo(frame, context=1):
 697     """Get information about a frame or traceback object.
 698
 699     A tuple of five things is returned: the filename, the line number of
 700     the current line, the function name, a list of lines of context from
 701     the source code, and the index of the current line within that list.
 702     The optional second argument specifies the number of lines of context
 703     to return, which are centered around the current line."""
 704     if istraceback(frame):
 705         frame = frame.tb_frame
 706     if not isframe(frame):
 707         raise TypeError, 'arg is not a frame or traceback object'
 708
 709     filename = getsourcefile(frame)
 710     lineno = getlineno(frame)
 711     if context > 0:
 712         start = lineno - 1 - context//2
 713         try:
 714             lines, lnum = findsource(frame)
 715         except IOError:
 716             lines = index = None
 717         else:
 718             start = max(start, 1)
 719             start = min(start, len(lines) - context)
 720             lines = lines[start:start+context]
 721             index = lineno - 1 - start
 722     else:
 723         lines = index = None
 724
 725     return (filename, lineno, frame.f_code.co_name, lines, index)
 726
 727 def getlineno(frame):
 728     """Get the line number from a frame object, allowing for optimization."""
 729     # Written by Marc-André Lemburg; revised by Jim Hugunin and Fredrik Lundh.
 730     lineno = frame.f_lineno
 731     code = frame.f_code
 732     if hasattr(code, 'co_lnotab'):
 733         table = code.co_lnotab
 734         lineno = code.co_firstlineno
 735         addr = 0
 736         for i in range(0, len(table), 2):
 737             addr = addr + ord(table[i])
 738             if addr > frame.f_lasti: break
 739             lineno = lineno + ord(table[i+1])
 740     return lineno
 741
 742 def getouterframes(frame, context=1):
 743     """Get a list of records for a frame and all higher (calling) frames.
 744
 745     Each record contains a frame object, filename, line number, function
 746     name, a list of lines of context, and index within the context."""
 747     framelist = []
 748     while frame:
 749         framelist.append((frame,) + getframeinfo(frame, context))
 750         frame = frame.f_back
 751     return framelist
 752
 753 def getinnerframes(tb, context=1):
 754     """Get a list of records for a traceback's frame and all lower frames.
 755
 756     Each record contains a frame object, filename, line number, function
 757     name, a list of lines of context, and index within the context."""
 758     framelist = []
 759     while tb:
 760         framelist.append((tb.tb_frame,) + getframeinfo(tb, context))
 761         tb = tb.tb_next
 762     return framelist
 763
 764 def currentframe():
 765     """Return the frame object for the caller's stack frame."""
 766     try:
 767         raise 'catch me'
 768     except:
 769         return sys.exc_traceback.tb_frame.f_back
 770
 771 if hasattr(sys, '_getframe'): currentframe = sys._getframe
 772
 773 def stack(context=1):
 774     """Return a list of records for the stack above the caller's frame."""
 775     return getouterframes(currentframe().f_back, context)
 776
 777 def trace(context=1):
 778     """Return a list of records for the stack below the current exception."""
 779     return getinnerframes(sys.exc_traceback, context)