    """Get useful information from live Python objects.

    This module encapsulates the interface provided by the internal special
    attributes (func_*, co_*, im_*, tb_*, etc.) in a friendlier fashion.
    It also provides some help for examining source code and class layout.

    Here are some of the useful functions provided by this module:

        ismodule(), isclass(), ismethod(), isfunction(), istraceback(),
            isframe(), iscode(), isbuiltin(), isroutine() - check object types
        getmembers() - get members of an object that satisfy a given condition

        getfile(), getsourcefile(), getsource() - find an object's source code
        getdoc(), getcomments() - get documentation on an object
        getmodule() - determine the module that an object came from
        getclasstree() - arrange classes so as to represent their hierarchy

        getargspec(), getargvalues() - get info about function arguments
        formatargspec(), formatargvalues() - format an argument spec
        getouterframes(), getinnerframes() - get info about frames
        currentframe() - get the current stack frame
        stack(), trace() - get info about frames on the stack or in a traceback

    """

    # This module is in the public domain.  No warranties.

    __author__ = 'Ka-Ping Yee <ping@lfw.org>'
    __date__ = '1 Jan 2001'

    import sys, os, types, re, dis, imp, tokenize

    # ----------------------------------------------------------- type-checking
    def ismodule(object):
        """Return true if the object is a module.

        Module objects provide these attributes:
            __doc__         documentation string
            __file__        filename (missing for built-in modules)"""
        return type(object) is types.ModuleType

    def isclass(object):
        """Return true if the object is a class.

        Class objects provide these attributes:
            __doc__         documentation string
            __module__      name of module in which this class was defined"""
        return type(object) is types.ClassType or hasattr(object, '__bases__')

    def ismethod(object):
        """Return true if the object is an instance method.

        Instance method objects provide these attributes:
            __doc__         documentation string
            __name__        name with which this method was defined
            im_class        class object in which this method belongs
            im_func         function object containing implementation of method
            im_self         instance to which this method is bound, or None"""
        return type(object) is types.MethodType

    def isfunction(object):
        """Return true if the object is a user-defined function.

        Function objects provide these attributes:
            __doc__         documentation string
            __name__        name with which this function was defined
            func_code       code object containing compiled function bytecode
            func_defaults   tuple of any default values for arguments
            func_doc        (same as __doc__)
            func_globals    global namespace in which this function was defined
            func_name       (same as __name__)"""
        return type(object) in (types.FunctionType, types.LambdaType)

    def istraceback(object):
        """Return true if the object is a traceback.

        Traceback objects provide these attributes:
            tb_frame        frame object at this level
            tb_lasti        index of last attempted instruction in bytecode
            tb_lineno       current line number in Python source code
            tb_next         next inner traceback object (called by this level)"""
        return type(object) is types.TracebackType

    def isframe(object):
        """Return true if the object is a frame object.

        Frame objects provide these attributes:
            f_back          next outer frame object (this frame's caller)
            f_builtins      built-in namespace seen by this frame
            f_code          code object being executed in this frame
            f_exc_traceback traceback if raised in this frame, or None
            f_exc_type      exception type if raised in this frame, or None
            f_exc_value     exception value if raised in this frame, or None
            f_globals       global namespace seen by this frame
            f_lasti         index of last attempted instruction in bytecode
            f_lineno        current line number in Python source code
            f_locals        local namespace seen by this frame
            f_restricted    0 or 1 if frame is in restricted execution mode
            f_trace         tracing function for this frame, or None"""
        return type(object) is types.FrameType

    def iscode(object):
        """Return true if the object is a code object.

        Code objects provide these attributes:
            co_argcount     number of arguments (not including * or ** args)
            co_code         string of raw compiled bytecode
            co_consts       tuple of constants used in the bytecode
            co_filename     name of file in which this code object was created
            co_firstlineno  number of first line in Python source code
            co_flags        bitmap: 1=optimized | 2=newlocals | 4=*arg | 8=**arg
            co_lnotab       encoded mapping of line numbers to bytecode indices
            co_name         name with which this code object was defined
            co_names        tuple of names of local variables
            co_nlocals      number of local variables
            co_stacksize    virtual machine stack space required
            co_varnames     tuple of names of arguments and local variables"""
        return type(object) is types.CodeType

    def isbuiltin(object):
        """Return true if the object is a built-in function or method.

        Built-in functions and methods provide these attributes:
            __doc__         documentation string
            __name__        original name of this function or method
            __self__        instance to which a method is bound, or None"""
        return type(object) is types.BuiltinFunctionType

    def isroutine(object):
        """Return true if the object is any kind of function or method."""
        return isbuiltin(object) or isfunction(object) or ismethod(object)

    def getmembers(object, predicate=None):
        """Return all members of an object as (name, value) pairs sorted by name.
        Optionally, only return members that satisfy a given predicate."""
        results = []
        for key in dir(object):
            value = getattr(object, key)
            if not predicate or predicate(value):
                results.append((key, value))
        results.sort()
        return results

    # -------------------------------------------------- source code extraction
    def indentsize(line):
        """Return the indent size, in spaces, at the start of a line of text."""
        expline = line.expandtabs()
        return len(expline) - len(expline.lstrip())

    def getdoc(object):
        """Get the documentation string for an object.

        All tabs are expanded to spaces.  To clean up docstrings that are
        indented to line up with blocks of code, any whitespace than can be
        uniformly removed from the second line onwards is removed."""
        if hasattr(object, '__doc__') and object.__doc__:
            lines = object.__doc__.expandtabs().split('\n')
            margin = None
            for line in lines[1:]:
                content = len(line.lstrip())
                if not content:
                    continue
                indent = len(line) - content
                if margin is None:
                    margin = indent
                else:
                    margin = min(margin, indent)
            if margin is not None:
                for i in range(1, len(lines)):
                    lines[i] = lines[i][margin:]
            return '\n'.join(lines)

    def getfile(object):
        """Work out which source or compiled file an object was defined in."""
        if ismodule(object):
            if hasattr(object, '__file__'):
                return object.__file__
            raise TypeError, 'arg is a built-in module'
        if isclass(object):
            object = sys.modules.get(object.__module__)
            if hasattr(object, '__file__'):
                return object.__file__
            raise TypeError, 'arg is a built-in class'
        if ismethod(object):
            object = object.im_func
        if isfunction(object):
            object = object.func_code
        if istraceback(object):
            object = object.tb_frame
        if isframe(object):
            object = object.f_code
        if iscode(object):
            return object.co_filename
        raise TypeError, 'arg is not a module, class, method, ' \
                         'function, traceback, frame, or code object'

    def getmoduleinfo(path):
        """Get the module name, suffix, mode, and module type for a given file."""
        filename = os.path.basename(path)
        suffixes = map(lambda (suffix, mode, mtype):
                       (-len(suffix), suffix, mode, mtype), imp.get_suffixes())
        suffixes.sort() # try longest suffixes first, in case they overlap
        for neglen, suffix, mode, mtype in suffixes:
            if filename[neglen:] == suffix:
                return filename[:neglen], suffix, mode, mtype

    def getmodulename(path):
        """Return the module name for a given file, or None."""
        info = getmoduleinfo(path)
        if info:
            return info[0]

    def getsourcefile(object):
        """Return the Python source file an object was defined in, if it exists."""
        filename = getfile(object)
        if filename[-4:].lower() in ('.pyc', '.pyo'):
            filename = filename[:-4] + '.py'
        for suffix, mode, kind in imp.get_suffixes():
            if 'b' in mode and filename[-len(suffix):].lower() == suffix:
                # Looks like a binary file.  We want to only return a text file.
                return None
        for path in sys.path:
            if os.path.exists(os.path.join(path, filename)):
                return os.path.join(path, filename)
        return None  # file was not found.

    def getabsfile(object):
        """Return an absolute path to the source or compiled file for an object.

        The idea is for each object to have a unique origin, so this routine
        normalizes the result as much as possible."""
        return os.path.normcase(
            os.path.abspath(getsourcefile(object) or getfile(object)))

    modulesbyfile = {}

    def getmodule(object):
        """Return the module an object was defined in, or None if not found."""
        if ismodule(object):
            return object
        if isclass(object):
            return sys.modules.get(object.__module__)
        try:
            file = getabsfile(object)
        except TypeError:
            return None
        if modulesbyfile.has_key(file):
            return sys.modules[modulesbyfile[file]]
        for module in sys.modules.values():
            if hasattr(module, '__file__'):
                modulesbyfile[getabsfile(module)] = module.__name__
        if modulesbyfile.has_key(file):
            return sys.modules[modulesbyfile[file]]
        main = sys.modules['__main__']
        if hasattr(main, object.__name__):
            mainobject = getattr(main, object.__name__)
            if mainobject is object:
                return main
        builtin = sys.modules['__builtin__']
        if hasattr(builtin, object.__name__):
            builtinobject = getattr(builtin, object.__name__)
            if builtinobject is object:
                return builtin

    def findsource(object):
        """Return the entire source file and starting line number for an object.

        The argument may be a module, class, method, function, traceback, frame,
        or code object.  The source code is returned as a list of all the lines
        in the file and the line number indexes a line in that list.  An IOError
        is raised if the source code cannot be retrieved."""
        try:
            file = open(getsourcefile(object))
        except (TypeError, IOError):
            raise IOError, 'could not get source code'
        lines = file.readlines()
        file.close()

        if ismodule(object):
            return lines, 0

        if isclass(object):
            name = object.__name__
            pat = re.compile(r'^\s*class\s*' + name + r'\b')
            for i in range(len(lines)):
                if pat.match(lines[i]):
                    return lines, i
            else:
                raise IOError, 'could not find class definition'

        if ismethod(object):
            object = object.im_func
        if isfunction(object):
            object = object.func_code
        if istraceback(object):
            object = object.tb_frame
        if isframe(object):
            object = object.f_code
        if iscode(object):
            if not hasattr(object, 'co_firstlineno'):
                raise IOError, 'could not find function definition'
            lnum = object.co_firstlineno - 1
            pat = re.compile(r'^\s*def\s')
            while lnum > 0:
                if pat.match(lines[lnum]):
                    break
                lnum -= 1
            return lines, lnum

    def getcomments(object):
        """Get lines of comments immediately preceding an object's source code."""
        try:
            lines, lnum = findsource(object)
        except IOError:
            return None

        if ismodule(object):
            # Look for a comment block at the top of the file.
            start = 0
            if lines and lines[0][:2] == '#!':
                start = 1
            while start < len(lines) and lines[start].strip() in ('', '#'):
                start += 1
            if start < len(lines) and lines[start][:1] == '#':
                comments = []
                end = start
                while end < len(lines) and lines[end][:1] == '#':
                    comments.append(lines[end].expandtabs())
                    end += 1
                return ''.join(comments)

        # Look for a preceding block of comments at the same indentation.
        elif lnum > 0:
            indent = indentsize(lines[lnum])
            end = lnum - 1
            if end >= 0 and lines[end].lstrip()[:1] == '#' \
                    and indentsize(lines[end]) == indent:
                comments = [lines[end].expandtabs().lstrip()]
                if end > 0:
                    end -= 1
                    comment = lines[end].expandtabs().lstrip()
                    while comment[:1] == '#' and indentsize(lines[end]) == indent:
                        comments[:0] = [comment]
                        end -= 1
                        if end < 0:
                            break
                        comment = lines[end].expandtabs().lstrip()
                while comments and comments[0].strip() == '#':
                    comments[:1] = []
                while comments and comments[-1].strip() == '#':
                    comments[-1:] = []
                return ''.join(comments)

    class ListReader:
        """Provide a readline() method to return lines from a list of strings."""

        def __init__(self, lines):
            self.lines = lines
            self.index = 0

        def readline(self):
            i = self.index
            if i < len(self.lines):
                self.index = i + 1
                return self.lines[i]
            else:
                return ''

    class EndOfBlock(Exception):
        pass

    class BlockFinder:
        """Provide a tokeneater() method to detect the end of a code block."""

        def __init__(self):
            self.indent = 0
            self.started = 0
            self.last = 0

        def tokeneater(self, type, token, (srow, scol), (erow, ecol), line):
            if not self.started:
                if type == tokenize.NAME:
                    self.started = 1
            elif type == tokenize.NEWLINE:
                self.last = srow
            elif type == tokenize.INDENT:
                self.indent += 1
            elif type == tokenize.DEDENT:
                self.indent -= 1
                if self.indent == 0:
                    raise EndOfBlock, self.last

    def getblock(lines):
        """Extract the block of code at the top of the given list of lines."""
        try:
            tokenize.tokenize(ListReader(lines).readline, BlockFinder().tokeneater)
        except EndOfBlock, eob:
            return lines[:eob.args[0]]

    def getsourcelines(object):
        """Return a list of source lines and starting line number for an object.

        The argument may be a module, class, method, function, traceback, frame,
        or code object.  The source code is returned as a list of the lines
        corresponding to the object and the line number indicates where in the
        original source file the first line of code was found.  An IOError is
        raised if the source code cannot be retrieved."""
        lines, lnum = findsource(object)

        if ismodule(object):
            return lines, 0
        else:
            return getblock(lines[lnum:]), lnum + 1

    def getsource(object):
        """Return the text of the source code for an object.

        The argument may be a module, class, method, function, traceback, frame,
        or code object.  The source code is returned as a single string.  An
        IOError is raised if the source code cannot be retrieved."""
        lines, lnum = getsourcelines(object)
        return ''.join(lines)

    # --------------------------------------------------- class tree extraction
    def walktree(classes, children, parent):
        """Recursive helper function for getclasstree()."""
        results = []
        classes.sort(lambda a, b: cmp(a.__name__, b.__name__))
        for c in classes:
            results.append((c, c.__bases__))
            if children.has_key(c):
                results.append(walktree(children[c], children, c))
        return results

    def getclasstree(classes, unique=0):
        """Arrange the given list of classes into a hierarchy of nested lists.

        Where a nested list appears, it contains classes derived from the class
        whose entry immediately precedes the list.  Each entry is a 2-tuple
        containing a class and a tuple of its base classes.  If the 'unique'
        argument is true, exactly one entry appears in the returned structure
        for each class in the given list.  Otherwise, classes using multiple
        inheritance and their descendants will appear multiple times."""
        children = {}
        roots = []
        for c in classes:
            if c.__bases__:
                for parent in c.__bases__:
                    if not children.has_key(parent):
                        children[parent] = []
                    children[parent].append(c)
                    if unique and parent in classes:
                        break
            elif c not in roots:
                roots.append(c)
        for parent in children.keys():
            if parent not in classes:
                roots.append(parent)
        return walktree(roots, children, None)

    # ------------------------------------------------ argument list extraction
    # These constants are from Python's compile.h.
    CO_OPTIMIZED, CO_NEWLOCALS, CO_VARARGS, CO_VARKEYWORDS = 1, 2, 4, 8

    def getargs(co):
        """Get information about the arguments accepted by a code object.

        Three things are returned: (args, varargs, varkw), where 'args' is
        a list of argument names (possibly containing nested lists), and
        'varargs' and 'varkw' are the names of the * and ** arguments or None."""
        if not iscode(co):
            raise TypeError, 'arg is not a code object'

        code = co.co_code
        nargs = co.co_argcount
        names = co.co_varnames
        args = list(names[:nargs])
        step = 0

        # The following acrobatics are for anonymous (tuple) arguments.
        for i in range(nargs):
            if args[i][:1] in ('', '.'):
                stack, remain, count = [], [], []
                while step < len(code):
                    op = ord(code[step])
                    step += 1
                    if op >= dis.HAVE_ARGUMENT:
                        opname = dis.opname[op]
                        value = ord(code[step]) + ord(code[step+1])*256
                        step += 2
                        if opname in ('UNPACK_TUPLE', 'UNPACK_SEQUENCE'):
                            remain.append(value)
                            count.append(value)
                        elif opname == 'STORE_FAST':
                            stack.append(names[value])
                            remain[-1] -= 1
                            while remain[-1] == 0:
                                remain.pop()
                                size = count.pop()
                                stack[-size:] = [stack[-size:]]
                                if not remain:
                                    break
                                remain[-1] -= 1
                            if not remain:
                                break
                args[i] = stack[0]

        varargs = None
        if co.co_flags & CO_VARARGS:
            varargs = co.co_varnames[nargs]
            nargs += 1
        varkw = None
        if co.co_flags & CO_VARKEYWORDS:
            varkw = co.co_varnames[nargs]
        return args, varargs, varkw

    def getargspec(func):
        """Get the names and default values of a function's arguments.

        A tuple of four things is returned: (args, varargs, varkw, defaults).
        'args' is a list of the argument names (it may contain nested lists).
        'varargs' and 'varkw' are the names of the * and ** arguments or None.
        'defaults' is an n-tuple of the default values of the last n arguments."""
        if not isfunction(func):
            raise TypeError, 'arg is not a Python function'
        args, varargs, varkw = getargs(func.func_code)
        return args, varargs, varkw, func.func_defaults

    def getargvalues(frame):
        """Get information about arguments passed into a particular frame.

        A tuple of four things is returned: (args, varargs, varkw, locals).
        'args' is a list of the argument names (it may contain nested lists).
        'varargs' and 'varkw' are the names of the * and ** arguments or None.
        'locals' is the locals dictionary of the given frame."""
        args, varargs, varkw = getargs(frame.f_code)
        return args, varargs, varkw, frame.f_locals

    def joinseq(seq):
        if len(seq) == 1:
            return '(' + seq[0] + ',)'
        else:
            return '(' + ', '.join(seq) + ')'

    def strseq(object, convert, join=joinseq):
        """Recursively walk a sequence, stringifying each element."""
        if type(object) in (types.ListType, types.TupleType):
            return join(map(lambda o, c=convert, j=join: strseq(o, c, j), object))
        else:
            return convert(object)

    def formatargspec(args, varargs=None, varkw=None, defaults=None,
            formatarg=str,
            formatvarargs=lambda name: '*' + name,
            formatvarkw=lambda name: '**' + name,
            formatvalue=lambda value: '=' + repr(value),
            join=joinseq):
        """Format an argument spec from the 4 values returned by getargspec.

        The first four arguments are (args, varargs, varkw, defaults).  The
        other four arguments are the corresponding optional formatting functions
        that are called to turn names and values into strings.  The ninth
        argument is an optional function to format the sequence of arguments."""
        specs = []
        if defaults:
            firstdefault = len(args) - len(defaults)
        for i in range(len(args)):
            spec = strseq(args[i], formatarg, join)
            if defaults and i >= firstdefault:
                spec += formatvalue(defaults[i - firstdefault])
            specs.append(spec)
        if varargs:
            specs.append(formatvarargs(varargs))
        if varkw:
            specs.append(formatvarkw(varkw))
        return '(' + ', '.join(specs) + ')'

    def formatargvalues(args, varargs, varkw, locals,
            formatarg=str,
            formatvarargs=lambda name: '*' + name,
            formatvarkw=lambda name: '**' + name,
            formatvalue=lambda value: '=' + repr(value),
            join=joinseq):
        """Format an argument spec from the 4 values returned by getargvalues.

        The first four arguments are (args, varargs, varkw, locals).  The
        next four arguments are the corresponding optional formatting functions
        that are called to turn names and values into strings.  The ninth
        argument is an optional function to format the sequence of arguments."""

        def convert(name, locals=locals,
                    formatarg=formatarg, formatvalue=formatvalue):
            return formatarg(name) + formatvalue(locals[name])
        specs = []
        for i in range(len(args)):
            specs.append(strseq(args[i], convert, join))
        if varargs:
            specs.append(formatvarargs(varargs) + formatvalue(locals[varargs]))
        if varkw:
            specs.append(formatvarkw(varkw) + formatvalue(locals[varkw]))
        return '(' + ', '.join(specs) + ')'

    # -------------------------------------------------- stack frame extraction
    def getframeinfo(frame, context=1):
        """Get information about a frame or traceback object.

        A tuple of five things is returned: the filename, the line number of
        the current line, the function name, a list of lines of context from
        the source code, and the index of the current line within that list.
        The optional second argument specifies the number of lines of context
        to return, which are centered around the current line."""
        if istraceback(frame):
            frame = frame.tb_frame
        if not isframe(frame):
            raise TypeError, 'arg is not a frame or traceback object'

        # prefer to give filename the actual source file but if
        # it does not exist, return the filename.
        filename = getsourcefile(frame) or getfile(frame)
        lineno = getlineno(frame)
        if context > 0:
            start = lineno - 1 - context/2
            try:
                lines, lnum = findsource(frame)
            except IOError:
                lines = index = None
            else:
                start = max(start, 1)
                start = min(start, len(lines) - context)
                lines = lines[start:start+context]
                index = lineno - 1 - start
        else:
            lines = index = None

        return (filename, lineno, frame.f_code.co_name, lines, index)

    def getlineno(frame):
        """Get the line number from a frame object, allowing for optimization."""
        # Written by Marc-Andre Lemburg; revised by Jim Hugunin and Fredrik Lundh.
        lineno = frame.f_lineno
        code = frame.f_code
        if hasattr(code, 'co_lnotab'):
            table = code.co_lnotab
            lineno = code.co_firstlineno
            addr = 0
            for i in range(0, len(table), 2):
                addr += ord(table[i])
                if addr > frame.f_lasti:
                    break
                lineno += ord(table[i+1])
        return lineno

    def getouterframes(frame, context=1):
        """Get a list of records for a frame and all higher (calling) frames.

        Each record contains a frame object, filename, line number, function
        name, a list of lines of context, and index within the context."""
        framelist = []
        while frame:
            framelist.append((frame,) + getframeinfo(frame, context))
            frame = frame.f_back
        return framelist

    def getinnerframes(tb, context=1):
        """Get a list of records for a traceback's frame and all lower frames.

        Each record contains a frame object, filename, line number, function
        name, a list of lines of context, and index within the context."""
        framelist = []
        while tb:
            framelist.append((tb.tb_frame,) + getframeinfo(tb, context))
            tb = tb.tb_next
        return framelist

    def currentframe():
        """Return the frame object for the caller's stack frame."""
        try:
            raise 'catch me'
        except:
            return sys.exc_info()[2].tb_frame.f_back

    if hasattr(sys, '_getframe'):
        currentframe = sys._getframe

    def stack(context=1):
        """Return a list of records for the stack above the caller's frame."""
        return getouterframes(currentframe().f_back, context)

    def trace(context=1):
        """Return a list of records for the stack below the current exception."""
        return getinnerframes(sys.exc_info()[2], context)