Backport function signature code from Python 3.3

Import PEP 362, function signatures, functionality from Python 3.3's
inspect module. Modifications have been made to make the code compatible
with Python 2.6 and 2.7, as well as 3.2+.

2 files changed, 1066 insertions, 0 deletions

diff --git a/funcsigs/__init__.py b/funcsigs/__init__.py
index 129426d..82d868d 100644
--- a/funcsigs/__init__.py
+++ b/funcsigs/__init__.py
@@ -1 +1,806 @@
+# Copyright 2001-2013 Python Software Foundation; All Rights Reserved
+"""Function signature objects for callables
+
+Back port of Python 3.3's function signature tools from the inspect module,
+modified to be compatible with Python 2.6, 2.7 and 3.2+.
+"""
+from __future__ import absolute_import, division, print_function
+import itertools
+import functools
+import re
+import types
+
+try:
+    from collections import OrderedDict
+except ImportError:
+    from funcsigs.odict import OrderedDict
+
 from funcsigs.version import __version__
+
+__all__ = ['BoundArguments', 'Parameter', 'Signature', 'signature']
+
+
+_WrapperDescriptor = type(type.__call__)
+_MethodWrapper = type(all.__call__)
+
+_NonUserDefinedCallables = (_WrapperDescriptor,
+                            _MethodWrapper,
+                            types.BuiltinFunctionType)
+
+
+def formatannotation(annotation, base_module=None):
+    if isinstance(annotation, type):
+        if annotation.__module__ in ('builtins', base_module):
+            return annotation.__name__
+        return annotation.__module__+'.'+annotation.__name__
+    return repr(annotation)
+
+
+def _get_user_defined_method(cls, method_name, *nested):
+    try:
+        meth = getattr(cls, method_name)
+        for name in nested:
+            meth = getattr(meth, name, meth)
+    except AttributeError:
+        return
+    else:
+        if not isinstance(meth, _NonUserDefinedCallables):
+            # Once '__signature__' will be added to 'C'-level
+            # callables, this check won't be necessary
+            return meth
+
+
+def signature(obj):
+    '''Get a signature object for the passed callable.'''
+
+    if not callable(obj):
+        raise TypeError('{0!r} is not a callable object'.format(obj))
+
+    if isinstance(obj, types.MethodType):
+        # In this case we skip the first parameter of the underlying
+        # function (usually `self` or `cls`).
+        sig = signature(obj.__func__)
+        return sig.replace(parameters=tuple(sig.parameters.values())[1:])
+
+    try:
+        sig = obj.__signature__
+    except AttributeError:
+        pass
+    else:
+        if sig is not None:
+            return sig
+
+    try:
+        # Was this function wrapped by a decorator?
+        wrapped = obj.__wrapped__
+    except AttributeError:
+        pass
+    else:
+        return signature(wrapped)
+
+    if isinstance(obj, types.FunctionType):
+        return Signature.from_function(obj)
+
+    if isinstance(obj, functools.partial):
+        sig = signature(obj.func)
+
+        new_params = OrderedDict(sig.parameters.items())
+
+        partial_args = obj.args or ()
+        partial_keywords = obj.keywords or {}
+        try:
+            ba = sig.bind_partial(*partial_args, **partial_keywords)
+        except TypeError as ex:
+            msg = 'partial object {0!r} has incorrect arguments'.format(obj)
+            raise ValueError(msg)
+
+        for arg_name, arg_value in ba.arguments.items():
+            param = new_params[arg_name]
+            if arg_name in partial_keywords:
+                # We set a new default value, because the following code
+                # is correct:
+                #
+                #   >>> def foo(a): print(a)
+                #   >>> print(partial(partial(foo, a=10), a=20)())
+                #   20
+                #   >>> print(partial(partial(foo, a=10), a=20)(a=30))
+                #   30
+                #
+                # So, with 'partial' objects, passing a keyword argument is
+                # like setting a new default value for the corresponding
+                # parameter
+                #
+                # We also mark this parameter with '_partial_kwarg'
+                # flag.  Later, in '_bind', the 'default' value of this
+                # parameter will be added to 'kwargs', to simulate
+                # the 'functools.partial' real call.
+                new_params[arg_name] = param.replace(default=arg_value,
+                                                     _partial_kwarg=True)
+
+            elif (param.kind not in (_VAR_KEYWORD, _VAR_POSITIONAL) and
+                            not param._partial_kwarg):
+                new_params.pop(arg_name)
+
+        return sig.replace(parameters=new_params.values())
+
+    sig = None
+    if isinstance(obj, type):
+        # obj is a class or a metaclass
+
+        # First, let's see if it has an overloaded __call__ defined
+        # in its metaclass
+        call = _get_user_defined_method(type(obj), '__call__')
+        if call is not None:
+            sig = signature(call)
+        else:
+            # Now we check if the 'obj' class has a '__new__' method
+            new = _get_user_defined_method(obj, '__new__')
+            if new is not None:
+                sig = signature(new)
+            else:
+                # Finally, we should have at least __init__ implemented
+                init = _get_user_defined_method(obj, '__init__')
+                if init is not None:
+                    sig = signature(init)
+    elif not isinstance(obj, _NonUserDefinedCallables):
+        # An object with __call__
+        # We also check that the 'obj' is not an instance of
+        # _WrapperDescriptor or _MethodWrapper to avoid
+        # infinite recursion (and even potential segfault)
+        call = _get_user_defined_method(type(obj), '__call__', 'im_func')
+        if call is not None:
+            sig = signature(call)
+
+    if sig is not None:
+        # For classes and objects we skip the first parameter of their
+        # __call__, __new__, or __init__ methods
+        return sig.replace(parameters=tuple(sig.parameters.values())[1:])
+
+    if isinstance(obj, types.BuiltinFunctionType):
+        # Raise a nicer error message for builtins
+        msg = 'no signature found for builtin function {0!r}'.format(obj)
+        raise ValueError(msg)
+
+    raise ValueError('callable {0!r} is not supported by signature'.format(obj))
+
+
+class _void(object):
+    '''A private marker - used in Parameter & Signature'''
+
+
+class _empty(object):
+    pass
+
+
+class _ParameterKind(int):
+    def __new__(self, *args, **kwargs):
+        obj = int.__new__(self, *args)
+        obj._name = kwargs['name']
+        return obj
+
+    def __str__(self):
+        return self._name
+
+    def __repr__(self):
+        return '<_ParameterKind: {0!r}>'.format(self._name)
+
+
+_POSITIONAL_ONLY        = _ParameterKind(0, name='POSITIONAL_ONLY')
+_POSITIONAL_OR_KEYWORD  = _ParameterKind(1, name='POSITIONAL_OR_KEYWORD')
+_VAR_POSITIONAL         = _ParameterKind(2, name='VAR_POSITIONAL')
+_KEYWORD_ONLY           = _ParameterKind(3, name='KEYWORD_ONLY')
+_VAR_KEYWORD            = _ParameterKind(4, name='VAR_KEYWORD')
+
+
+class Parameter(object):
+    '''Represents a parameter in a function signature.
+
+    Has the following public attributes:
+
+    * name : str
+        The name of the parameter as a string.
+    * default : object
+        The default value for the parameter if specified.  If the
+        parameter has no default value, this attribute is not set.
+    * annotation
+        The annotation for the parameter if specified.  If the
+        parameter has no annotation, this attribute is not set.
+    * kind : str
+        Describes how argument values are bound to the parameter.
+        Possible values: `Parameter.POSITIONAL_ONLY`,
+        `Parameter.POSITIONAL_OR_KEYWORD`, `Parameter.VAR_POSITIONAL`,
+        `Parameter.KEYWORD_ONLY`, `Parameter.VAR_KEYWORD`.
+    '''
+
+    __slots__ = ('_name', '_kind', '_default', '_annotation', '_partial_kwarg')
+
+    POSITIONAL_ONLY         = _POSITIONAL_ONLY
+    POSITIONAL_OR_KEYWORD   = _POSITIONAL_OR_KEYWORD
+    VAR_POSITIONAL          = _VAR_POSITIONAL
+    KEYWORD_ONLY            = _KEYWORD_ONLY
+    VAR_KEYWORD             = _VAR_KEYWORD
+
+    empty = _empty
+
+    def __init__(self, name, kind, default=_empty, annotation=_empty,
+                 _partial_kwarg=False):
+
+        if kind not in (_POSITIONAL_ONLY, _POSITIONAL_OR_KEYWORD,
+                        _VAR_POSITIONAL, _KEYWORD_ONLY, _VAR_KEYWORD):
+            raise ValueError("invalid value for 'Parameter.kind' attribute")
+        self._kind = kind
+
+        if default is not _empty:
+            if kind in (_VAR_POSITIONAL, _VAR_KEYWORD):
+                msg = '{0} parameters cannot have default values'.format(kind)
+                raise ValueError(msg)
+        self._default = default
+        self._annotation = annotation
+
+        if name is None:
+            if kind != _POSITIONAL_ONLY:
+                raise ValueError("None is not a valid name for a "
+                                 "non-positional-only parameter")
+            self._name = name
+        else:
+            name = str(name)
+            if kind != _POSITIONAL_ONLY and not re.match(r'[a-z_]\w*$', name, re.I):
+                msg = '{0!r} is not a valid parameter name'.format(name)
+                raise ValueError(msg)
+            self._name = name
+
+        self._partial_kwarg = _partial_kwarg
+
+    @property
+    def name(self):
+        return self._name
+
+    @property
+    def default(self):
+        return self._default
+
+    @property
+    def annotation(self):
+        return self._annotation
+
+    @property
+    def kind(self):
+        return self._kind
+
+    def replace(self, name=_void, kind=_void, annotation=_void,
+                default=_void, _partial_kwarg=_void):
+        '''Creates a customized copy of the Parameter.'''
+
+        if name is _void:
+            name = self._name
+
+        if kind is _void:
+            kind = self._kind
+
+        if annotation is _void:
+            annotation = self._annotation
+
+        if default is _void:
+            default = self._default
+
+        if _partial_kwarg is _void:
+            _partial_kwarg = self._partial_kwarg
+
+        return type(self)(name, kind, default=default, annotation=annotation,
+                          _partial_kwarg=_partial_kwarg)
+
+    def __str__(self):
+        kind = self.kind
+
+        formatted = self._name
+        if kind == _POSITIONAL_ONLY:
+            if formatted is None:
+                formatted = ''
+            formatted = '<{0}>'.format(formatted)
+
+        # Add annotation and default value
+        if self._annotation is not _empty:
+            formatted = '{0}:{1}'.format(formatted,
+                                       formatannotation(self._annotation))
+
+        if self._default is not _empty:
+            formatted = '{0}={1}'.format(formatted, repr(self._default))
+
+        if kind == _VAR_POSITIONAL:
+            formatted = '*' + formatted
+        elif kind == _VAR_KEYWORD:
+            formatted = '**' + formatted
+
+        return formatted
+
+    def __repr__(self):
+        return '<{0} at {1:#x} {2!r}>'.format(self.__class__.__name__,
+                                           id(self), self.name)
+
+    def __hash__(self):
+        msg = "unhashable type: '{0}'".format(self.__class__.__name__)
+        raise TypeError(msg)
+
+    def __eq__(self, other):
+        return (issubclass(other.__class__, Parameter) and
+                self._name == other._name and
+                self._kind == other._kind and
+                self._default == other._default and
+                self._annotation == other._annotation)
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+
+class BoundArguments(object):
+    '''Result of `Signature.bind` call.  Holds the mapping of arguments
+    to the function's parameters.
+
+    Has the following public attributes:
+
+    * arguments : OrderedDict
+        An ordered mutable mapping of parameters' names to arguments' values.
+        Does not contain arguments' default values.
+    * signature : Signature
+        The Signature object that created this instance.
+    * args : tuple
+        Tuple of positional arguments values.
+    * kwargs : dict
+        Dict of keyword arguments values.
+    '''
+
+    def __init__(self, signature, arguments):
+        self.arguments = arguments
+        self._signature = signature
+
+    @property
+    def signature(self):
+        return self._signature
+
+    @property
+    def args(self):
+        args = []
+        for param_name, param in self._signature.parameters.items():
+            if (param.kind in (_VAR_KEYWORD, _KEYWORD_ONLY) or
+                                                    param._partial_kwarg):
+                # Keyword arguments mapped by 'functools.partial'
+                # (Parameter._partial_kwarg is True) are mapped
+                # in 'BoundArguments.kwargs', along with VAR_KEYWORD &
+                # KEYWORD_ONLY
+                break
+
+            try:
+                arg = self.arguments[param_name]
+            except KeyError:
+                # We're done here. Other arguments
+                # will be mapped in 'BoundArguments.kwargs'
+                break
+            else:
+                if param.kind == _VAR_POSITIONAL:
+                    # *args
+                    args.extend(arg)
+                else:
+                    # plain argument
+                    args.append(arg)
+
+        return tuple(args)
+
+    @property
+    def kwargs(self):
+        kwargs = {}
+        kwargs_started = False
+        for param_name, param in self._signature.parameters.items():
+            if not kwargs_started:
+                if (param.kind in (_VAR_KEYWORD, _KEYWORD_ONLY) or
+                                                param._partial_kwarg):
+                    kwargs_started = True
+                else:
+                    if param_name not in self.arguments:
+                        kwargs_started = True
+                        continue
+
+            if not kwargs_started:
+                continue
+
+            try:
+                arg = self.arguments[param_name]
+            except KeyError:
+                pass
+            else:
+                if param.kind == _VAR_KEYWORD:
+                    # **kwargs
+                    kwargs.update(arg)
+                else:
+                    # plain keyword argument
+                    kwargs[param_name] = arg
+
+        return kwargs
+
+    def __hash__(self):
+        msg = "unhashable type: '{0}'".format(self.__class__.__name__)
+        raise TypeError(msg)
+
+    def __eq__(self, other):
+        return (issubclass(other.__class__, BoundArguments) and
+                self.signature == other.signature and
+                self.arguments == other.arguments)
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+
+class Signature(object):
+    '''A Signature object represents the overall signature of a function.
+    It stores a Parameter object for each parameter accepted by the
+    function, as well as information specific to the function itself.
+
+    A Signature object has the following public attributes and methods:
+
+    * parameters : OrderedDict
+        An ordered mapping of parameters' names to the corresponding
+        Parameter objects (keyword-only arguments are in the same order
+        as listed in `code.co_varnames`).
+    * return_annotation : object
+        The annotation for the return type of the function if specified.
+        If the function has no annotation for its return type, this
+        attribute is not set.
+    * bind(*args, **kwargs) -> BoundArguments
+        Creates a mapping from positional and keyword arguments to
+        parameters.
+    * bind_partial(*args, **kwargs) -> BoundArguments
+        Creates a partial mapping from positional and keyword arguments
+        to parameters (simulating 'functools.partial' behavior.)
+    '''
+
+    __slots__ = ('_return_annotation', '_parameters')
+
+    _parameter_cls = Parameter
+    _bound_arguments_cls = BoundArguments
+
+    empty = _empty
+
+    def __init__(self, parameters=None, return_annotation=_empty,
+                 __validate_parameters__=True):
+        '''Constructs Signature from the given list of Parameter
+        objects and 'return_annotation'.  All arguments are optional.
+        '''
+
+        if parameters is None:
+            params = OrderedDict()
+        else:
+            if __validate_parameters__:
+                params = OrderedDict()
+                top_kind = _POSITIONAL_ONLY
+
+                for idx, param in enumerate(parameters):
+                    kind = param.kind
+                    if kind < top_kind:
+                        msg = 'wrong parameter order: {0} before {1}'
+                        msg = msg.format(top_kind, param.kind)
+                        raise ValueError(msg)
+                    else:
+                        top_kind = kind
+
+                    name = param.name
+                    if name is None:
+                        name = str(idx)
+                        param = param.replace(name=name)
+
+                    if name in params:
+                        msg = 'duplicate parameter name: {0!r}'.format(name)
+                        raise ValueError(msg)
+                    params[name] = param
+            else:
+                params = OrderedDict(((param.name, param)
+                                                for param in parameters))
+
+        self._parameters = params
+        self._return_annotation = return_annotation
+
+    @classmethod
+    def from_function(cls, func):
+        '''Constructs Signature for the given python function'''
+
+        if not isinstance(func, types.FunctionType):
+            raise TypeError('{0!r} is not a Python function'.format(func))
+
+        Parameter = cls._parameter_cls
+
+        # Parameter information.
+        func_code = func.__code__
+        pos_count = func_code.co_argcount
+        arg_names = func_code.co_varnames
+        positional = tuple(arg_names[:pos_count])
+        keyword_only_count = getattr(func_code, 'co_kwonlyargcount', 0)
+        keyword_only = arg_names[pos_count:(pos_count + keyword_only_count)]
+        annotations = getattr(func, '__annotations__', {})
+        defaults = func.__defaults__
+        kwdefaults = getattr(func, '__kwdefaults__', None)
+
+        if defaults:
+            pos_default_count = len(defaults)
+        else:
+            pos_default_count = 0
+
+        parameters = []
+
+        # Non-keyword-only parameters w/o defaults.
+        non_default_count = pos_count - pos_default_count
+        for name in positional[:non_default_count]:
+            annotation = annotations.get(name, _empty)
+            parameters.append(Parameter(name, annotation=annotation,
+                                        kind=_POSITIONAL_OR_KEYWORD))
+
+        # ... w/ defaults.
+        for offset, name in enumerate(positional[non_default_count:]):
+            annotation = annotations.get(name, _empty)
+            parameters.append(Parameter(name, annotation=annotation,
+                                        kind=_POSITIONAL_OR_KEYWORD,
+                                        default=defaults[offset]))
+
+        # *args
+        if func_code.co_flags & 0x04:
+            name = arg_names[pos_count + keyword_only_count]
+            annotation = annotations.get(name, _empty)
+            parameters.append(Parameter(name, annotation=annotation,
+                                        kind=_VAR_POSITIONAL))
+
+        # Keyword-only parameters.
+        for name in keyword_only:
+            default = _empty
+            if kwdefaults is not None:
+                default = kwdefaults.get(name, _empty)
+
+            annotation = annotations.get(name, _empty)
+            parameters.append(Parameter(name, annotation=annotation,
+                                        kind=_KEYWORD_ONLY,
+                                        default=default))
+        # **kwargs
+        if func_code.co_flags & 0x08:
+            index = pos_count + keyword_only_count
+            if func_code.co_flags & 0x04:
+                index += 1
+
+            name = arg_names[index]
+            annotation = annotations.get(name, _empty)
+            parameters.append(Parameter(name, annotation=annotation,
+                                        kind=_VAR_KEYWORD))
+
+        return cls(parameters,
+                   return_annotation=annotations.get('return', _empty),
+                   __validate_parameters__=False)
+
+    @property
+    def parameters(self):
+        try:
+            return types.MappingProxyType(self._parameters)
+        except AttributeError:
+            return OrderedDict(self._parameters.items())
+
+    @property
+    def return_annotation(self):
+        return self._return_annotation
+
+    def replace(self, parameters=_void, return_annotation=_void):
+        '''Creates a customized copy of the Signature.
+        Pass 'parameters' and/or 'return_annotation' arguments
+        to override them in the new copy.
+        '''
+
+        if parameters is _void:
+            parameters = self.parameters.values()
+
+        if return_annotation is _void:
+            return_annotation = self._return_annotation
+
+        return type(self)(parameters,
+                          return_annotation=return_annotation)
+
+    def __hash__(self):
+        msg = "unhashable type: '{0}'".format(self.__class__.__name__)
+        raise TypeError(msg)
+
+    def __eq__(self, other):
+        if (not issubclass(type(other), Signature) or
+                    self.return_annotation != other.return_annotation or
+                    len(self.parameters) != len(other.parameters)):
+            return False
+
+        other_positions = dict((param, idx)
+                           for idx, param in enumerate(other.parameters.keys()))
+
+        for idx, (param_name, param) in enumerate(self.parameters.items()):
+            if param.kind == _KEYWORD_ONLY:
+                try:
+                    other_param = other.parameters[param_name]
+                except KeyError:
+                    return False
+                else:
+                    if param != other_param:
+                        return False
+            else:
+                try:
+                    other_idx = other_positions[param_name]
+                except KeyError:
+                    return False
+                else:
+                    if (idx != other_idx or
+                                    param != other.parameters[param_name]):
+                        return False
+
+        return True
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+    def _bind(self, args, kwargs, partial=False):
+        '''Private method.  Don't use directly.'''
+
+        arguments = OrderedDict()
+
+        parameters = iter(self.parameters.values())
+        parameters_ex = ()
+        arg_vals = iter(args)
+
+        if partial:
+            # Support for binding arguments to 'functools.partial' objects.
+            # See 'functools.partial' case in 'signature()' implementation
+            # for details.
+            for param_name, param in self.parameters.items():
+                if (param._partial_kwarg and param_name not in kwargs):
+                    # Simulating 'functools.partial' behavior
+                    kwargs[param_name] = param.default
+
+        while True:
+            # Let's iterate through the positional arguments and corresponding
+            # parameters
+            try:
+                arg_val = next(arg_vals)
+            except StopIteration:
+                # No more positional arguments
+                try:
+                    param = next(parameters)
+                except StopIteration:
+                    # No more parameters. That's it. Just need to check that
+                    # we have no `kwargs` after this while loop
+                    break
+                else:
+                    if param.kind == _VAR_POSITIONAL:
+                        # That's OK, just empty *args.  Let's start parsing
+                        # kwargs
+                        break
+                    elif param.name in kwargs:
+                        if param.kind == _POSITIONAL_ONLY:
+                            msg = '{arg!r} parameter is positional only, ' \
+                                  'but was passed as a keyword'
+                            msg = msg.format(arg=param.name)
+                            raise TypeError(msg)
+                        parameters_ex = (param,)
+                        break
+                    elif (param.kind == _VAR_KEYWORD or
+                                                param.default is not _empty):
+                        # That's fine too - we have a default value for this
+                        # parameter.  So, lets start parsing `kwargs`, starting
+                        # with the current parameter
+                        parameters_ex = (param,)
+                        break
+                    else:
+                        if partial:
+                            parameters_ex = (param,)
+                            break
+                        else:
+                            msg = '{arg!r} parameter lacking default value'
+                            msg = msg.format(arg=param.name)
+                            raise TypeError(msg)
+            else:
+                # We have a positional argument to process
+                try:
+                    param = next(parameters)
+                except StopIteration:
+                    raise TypeError('too many positional arguments')
+                else:
+                    if param.kind in (_VAR_KEYWORD, _KEYWORD_ONLY):
+                        # Looks like we have no parameter for this positional
+                        # argument
+                        raise TypeError('too many positional arguments')
+
+                    if param.kind == _VAR_POSITIONAL:
+                        # We have an '*args'-like argument, let's fill it with
+                        # all positional arguments we have left and move on to
+                        # the next phase
+                        values = [arg_val]
+                        values.extend(arg_vals)
+                        arguments[param.name] = tuple(values)
+                        break
+
+                    if param.name in kwargs:
+                        raise TypeError('multiple values for argument '
+                                        '{arg!r}'.format(arg=param.name))
+
+                    arguments[param.name] = arg_val
+
+        # Now, we iterate through the remaining parameters to process
+        # keyword arguments
+        kwargs_param = None
+        for param in itertools.chain(parameters_ex, parameters):
+            if param.kind == _POSITIONAL_ONLY:
+                # This should never happen in case of a properly built
+                # Signature object (but let's have this check here
+                # to ensure correct behaviour just in case)
+                raise TypeError('{arg!r} parameter is positional only, '
+                                'but was passed as a keyword'. \
+                                format(arg=param.name))
+
+            if param.kind == _VAR_KEYWORD:
+                # Memorize that we have a '**kwargs'-like parameter
+                kwargs_param = param
+                continue
+
+            param_name = param.name
+            try:
+                arg_val = kwargs.pop(param_name)
+            except KeyError:
+                # We have no value for this parameter.  It's fine though,
+                # if it has a default value, or it is an '*args'-like
+                # parameter, left alone by the processing of positional
+                # arguments.
+                if (not partial and param.kind != _VAR_POSITIONAL and
+                                                    param.default is _empty):
+                    raise TypeError('{arg!r} parameter lacking default value'. \
+                                    format(arg=param_name))
+
+            else:
+                arguments[param_name] = arg_val
+
+        if kwargs:
+            if kwargs_param is not None:
+                # Process our '**kwargs'-like parameter
+                arguments[kwargs_param.name] = kwargs
+            else:
+                raise TypeError('too many keyword arguments')
+
+        return self._bound_arguments_cls(self, arguments)
+
+    def bind(self, *args, **kwargs):
+        '''Get a BoundArguments object, that maps the passed `args`
+        and `kwargs` to the function's signature.  Raises `TypeError`
+        if the passed arguments can not be bound.
+        '''
+        return self._bind(args, kwargs)
+
+    def bind_partial(self, *args, **kwargs):
+        '''Get a BoundArguments object, that partially maps the
+        passed `args` and `kwargs` to the function's signature.
+        Raises `TypeError` if the passed arguments can not be bound.
+        '''
+        return self._bind(args, kwargs, partial=True)
+
+    def __str__(self):
+        result = []
+        render_kw_only_separator = True
+        for idx, param in enumerate(self.parameters.values()):
+            formatted = str(param)
+
+            kind = param.kind
+            if kind == _VAR_POSITIONAL:
+                # OK, we have an '*args'-like parameter, so we won't need
+                # a '*' to separate keyword-only arguments
+                render_kw_only_separator = False
+            elif kind == _KEYWORD_ONLY and render_kw_only_separator:
+                # We have a keyword-only parameter to render and we haven't
+                # rendered an '*args'-like parameter before, so add a '*'
+                # separator to the parameters list ("foo(arg1, *, arg2)" case)
+                result.append('*')
+                # This condition should be only triggered once, so
+                # reset the flag
+                render_kw_only_separator = False
+
+            result.append(formatted)
+
+        rendered = '({0})'.format(', '.join(result))
+
+        if self.return_annotation is not _empty:
+            anno = formatannotation(self.return_annotation)
+            rendered += ' -> {0}'.format(anno)
+
+        return rendered
diff --git a/funcsigs/odict.py b/funcsigs/odict.py
new file mode 100644
index 0000000..6221e97
--- /dev/null
+++ b/funcsigs/odict.py
@@ -0,0 +1,261 @@
+# Backport of OrderedDict() class that runs on Python 2.4, 2.5, 2.6, 2.7 and pypy.
+# Passes Python2.7's test suite and incorporates all the latest updates.
+# Copyright 2009 Raymond Hettinger
+# http://code.activestate.com/recipes/576693/
+"Ordered dictionary"
+
+try:
+    from thread import get_ident as _get_ident
+except ImportError:
+    from dummy_thread import get_ident as _get_ident
+
+try:
+    from _abcoll import KeysView, ValuesView, ItemsView
+except ImportError:
+    pass
+
+
+class OrderedDict(dict):
+    'Dictionary that remembers insertion order'
+    # An inherited dict maps keys to values.
+    # The inherited dict provides __getitem__, __len__, __contains__, and get.
+    # The remaining methods are order-aware.
+    # Big-O running times for all methods are the same as for regular dictionaries.
+
+    # The internal self.__map dictionary maps keys to links in a doubly linked list.
+    # The circular doubly linked list starts and ends with a sentinel element.
+    # The sentinel element never gets deleted (this simplifies the algorithm).
+    # Each link is stored as a list of length three:  [PREV, NEXT, KEY].
+
+    def __init__(self, *args, **kwds):
+        '''Initialize an ordered dictionary.  Signature is the same as for
+        regular dictionaries, but keyword arguments are not recommended
+        because their insertion order is arbitrary.
+
+        '''
+        if len(args) > 1:
+            raise TypeError('expected at most 1 arguments, got %d' % len(args))
+        try:
+            self.__root
+        except AttributeError:
+            self.__root = root = []                     # sentinel node
+            root[:] = [root, root, None]
+            self.__map = {}
+        self.__update(*args, **kwds)
+
+    def __setitem__(self, key, value, dict_setitem=dict.__setitem__):
+        'od.__setitem__(i, y) <==> od[i]=y'
+        # Setting a new item creates a new link which goes at the end of the linked
+        # list, and the inherited dictionary is updated with the new key/value pair.
+        if key not in self:
+            root = self.__root
+            last = root[0]
+            last[1] = root[0] = self.__map[key] = [last, root, key]
+        dict_setitem(self, key, value)
+
+    def __delitem__(self, key, dict_delitem=dict.__delitem__):
+        'od.__delitem__(y) <==> del od[y]'
+        # Deleting an existing item uses self.__map to find the link which is
+        # then removed by updating the links in the predecessor and successor nodes.
+        dict_delitem(self, key)
+        link_prev, link_next, key = self.__map.pop(key)
+        link_prev[1] = link_next
+        link_next[0] = link_prev
+
+    def __iter__(self):
+        'od.__iter__() <==> iter(od)'
+        root = self.__root
+        curr = root[1]
+        while curr is not root:
+            yield curr[2]
+            curr = curr[1]
+
+    def __reversed__(self):
+        'od.__reversed__() <==> reversed(od)'
+        root = self.__root
+        curr = root[0]
+        while curr is not root:
+            yield curr[2]
+            curr = curr[0]
+
+    def clear(self):
+        'od.clear() -> None.  Remove all items from od.'
+        try:
+            for node in self.__map.itervalues():
+                del node[:]
+            root = self.__root
+            root[:] = [root, root, None]
+            self.__map.clear()
+        except AttributeError:
+            pass
+        dict.clear(self)
+
+    def popitem(self, last=True):
+        '''od.popitem() -> (k, v), return and remove a (key, value) pair.
+        Pairs are returned in LIFO order if last is true or FIFO order if false.
+
+        '''
+        if not self:
+            raise KeyError('dictionary is empty')
+        root = self.__root
+        if last:
+            link = root[0]
+            link_prev = link[0]
+            link_prev[1] = root
+            root[0] = link_prev
+        else:
+            link = root[1]
+            link_next = link[1]
+            root[1] = link_next
+            link_next[0] = root
+        key = link[2]
+        del self.__map[key]
+        value = dict.pop(self, key)
+        return key, value
+
+    # -- the following methods do not depend on the internal structure --
+
+    def keys(self):
+        'od.keys() -> list of keys in od'
+        return list(self)
+
+    def values(self):
+        'od.values() -> list of values in od'
+        return [self[key] for key in self]
+
+    def items(self):
+        'od.items() -> list of (key, value) pairs in od'
+        return [(key, self[key]) for key in self]
+
+    def iterkeys(self):
+        'od.iterkeys() -> an iterator over the keys in od'
+        return iter(self)
+
+    def itervalues(self):
+        'od.itervalues -> an iterator over the values in od'
+        for k in self:
+            yield self[k]
+
+    def iteritems(self):
+        'od.iteritems -> an iterator over the (key, value) items in od'
+        for k in self:
+            yield (k, self[k])
+
+    def update(*args, **kwds):
+        '''od.update(E, **F) -> None.  Update od from dict/iterable E and F.
+
+        If E is a dict instance, does:           for k in E: od[k] = E[k]
+        If E has a .keys() method, does:         for k in E.keys(): od[k] = E[k]
+        Or if E is an iterable of items, does:   for k, v in E: od[k] = v
+        In either case, this is followed by:     for k, v in F.items(): od[k] = v
+
+        '''
+        if len(args) > 2:
+            raise TypeError('update() takes at most 2 positional '
+                            'arguments (%d given)' % (len(args),))
+        elif not args:
+            raise TypeError('update() takes at least 1 argument (0 given)')
+        self = args[0]
+        # Make progressively weaker assumptions about "other"
+        other = ()
+        if len(args) == 2:
+            other = args[1]
+        if isinstance(other, dict):
+            for key in other:
+                self[key] = other[key]
+        elif hasattr(other, 'keys'):
+            for key in other.keys():
+                self[key] = other[key]
+        else:
+            for key, value in other:
+                self[key] = value
+        for key, value in kwds.items():
+            self[key] = value
+
+    __update = update  # let subclasses override update without breaking __init__
+
+    __marker = object()
+
+    def pop(self, key, default=__marker):
+        '''od.pop(k[,d]) -> v, remove specified key and return the corresponding value.
+        If key is not found, d is returned if given, otherwise KeyError is raised.
+
+        '''
+        if key in self:
+            result = self[key]
+            del self[key]
+            return result
+        if default is self.__marker:
+            raise KeyError(key)
+        return default
+
+    def setdefault(self, key, default=None):
+        'od.setdefault(k[,d]) -> od.get(k,d), also set od[k]=d if k not in od'
+        if key in self:
+            return self[key]
+        self[key] = default
+        return default
+
+    def __repr__(self, _repr_running={}):
+        'od.__repr__() <==> repr(od)'
+        call_key = id(self), _get_ident()
+        if call_key in _repr_running:
+            return '...'
+        _repr_running[call_key] = 1
+        try:
+            if not self:
+                return '%s()' % (self.__class__.__name__,)
+            return '%s(%r)' % (self.__class__.__name__, self.items())
+        finally:
+            del _repr_running[call_key]
+
+    def __reduce__(self):
+        'Return state information for pickling'
+        items = [[k, self[k]] for k in self]
+        inst_dict = vars(self).copy()
+        for k in vars(OrderedDict()):
+            inst_dict.pop(k, None)
+        if inst_dict:
+            return (self.__class__, (items,), inst_dict)
+        return self.__class__, (items,)
+
+    def copy(self):
+        'od.copy() -> a shallow copy of od'
+        return self.__class__(self)
+
+    @classmethod
+    def fromkeys(cls, iterable, value=None):
+        '''OD.fromkeys(S[, v]) -> New ordered dictionary with keys from S
+        and values equal to v (which defaults to None).
+
+        '''
+        d = cls()
+        for key in iterable:
+            d[key] = value
+        return d
+
+    def __eq__(self, other):
+        '''od.__eq__(y) <==> od==y.  Comparison to another OD is order-sensitive
+        while comparison to a regular mapping is order-insensitive.
+
+        '''
+        if isinstance(other, OrderedDict):
+            return len(self)==len(other) and self.items() == other.items()
+        return dict.__eq__(self, other)
+
+    def __ne__(self, other):
+        return not self == other
+
+    # -- the following methods are only used in Python 2.7 --
+
+    def viewkeys(self):
+        "od.viewkeys() -> a set-like object providing a view on od's keys"
+        return KeysView(self)
+
+    def viewvalues(self):
+        "od.viewvalues() -> an object providing a view on od's values"
+        return ValuesView(self)
+
+    def viewitems(self):
+        "od.viewitems() -> a set-like object providing a view on od's items"
+        return ItemsView(self)