Get widgets from function annotations and default arguments.

Also, preserve the order of function parameters from the signature where
possible.

This uses a backport of the Python 3.3 signature machinery that @minrk
found and improved.

IPython/utils/signatures.py

@@ -0,0 +1,819
+"""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+.
+"""
+
+#-----------------------------------------------------------------------------
+#  Python 3.3 stdlib inspect.py is public domain
+# 
+#  Backports Copyright (C) 2013 Aaron Iles
+#  Used under Apache License Version 2.0
+#
+#  Further Changes are Copyright (C) 2013 The IPython Development Team
+#
+#  Distributed under the terms of the BSD License.  The full license is in
+#  the file COPYING, distributed as part of this software.
+#-----------------------------------------------------------------------------
+
+from __future__ import absolute_import, division, print_function
+import itertools
+import functools
+import re
+import types
+
+
+# patch for single-file
+# we don't support 2.6, so we can just import OrderedDict
+from collections import OrderedDict
+
+__version__ = '0.3'
+# end patch
+
+__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', '__builtin__', base_module):
+            return annotation.__name__
+        return annotation.__module__+'.'+annotation.__name__
+    return repr(annotation)
+
+
+def _get_user_defined_method(cls, method_name, *nested):
+    try:
+        if cls is type:
+            return
+        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:
+        return sig
+
+    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

IPython/html/widgets/interact.py

@@ -1,139 +1,190
 """Interact with functions using widgets.
 """
 
 #-----------------------------------------------------------------------------
 # Copyright (c) 2013, the IPython Development Team.
 #
 # Distributed under the terms of the Modified BSD License.
 #
 # The full license is in the file COPYING.txt, distributed with this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
+try:  # Python >= 3.3
+    from inspect import signature, Parameter
+except ImportError:
+    from IPython.utils.signatures import signature, Parameter
+
 from IPython.html.widgets import (Widget, TextWidget,
     FloatSliderWidget, IntSliderWidget, CheckboxWidget, DropdownWidget,
     ContainerWidget)
 from IPython.display import display, clear_output
 from IPython.utils.py3compat import string_types, unicode_type
 
 #-----------------------------------------------------------------------------
 # Classes and Functions
 #-----------------------------------------------------------------------------
 
 
 def _matches(o, pattern):
     if not len(o) == len(pattern):
         return False
     comps = zip(o,pattern)
     return all(isinstance(obj,kind) for obj,kind in comps)
 
 
 def _get_min_max_value(min, max, value):
     """Return min, max, value given input values with possible None."""
     if value is None:
         if not max > min:
             raise ValueError('max must be greater than min: (min={0}, max={1})'.format(min, max))
         value = min + abs(min-max)/2
         value = type(min)(value)
     elif min is None and max is None:
         if value == 0.0:
             min, max, value = 0.0, 1.0, 0.5
         elif value == 0:
             min, max, value = 0, 1, 0
         elif isinstance(value, float):
             min, max = -value, 3.0*value
         elif isinstance(value, int):
             min, max = -value, 3*value
         else:
-            raise TypeError('expected a number, got: %r' % number)
+            raise TypeError('expected a number, got: %r' % value)
     else:
         raise ValueError('unable to infer range, value from: ({0}, {1}, {2})'.format(min, max, value))
     return min, max, value
 
-
-def _widget_abbrev(o):
+def _widget_abbrev_single_value(o):
+    """Make widgets from single values, which can be used written as parameter defaults."""
     if isinstance(o, string_types):
         return TextWidget(value=unicode_type(o))
     elif isinstance(o, dict):
         labels = [unicode_type(k) for k in o]
         values = o.values()
         w = DropdownWidget(value=values[0], values=values, labels=labels)
         return w
     # Special case float and int == 0.0
     # get_range(value):
     elif isinstance(o, bool):
         return CheckboxWidget(value=o)
     elif isinstance(o, float):
         min, max, value = _get_min_max_value(None, None, o)
         return FloatSliderWidget(value=o, min=min, max=max)
     elif isinstance(o, int):
         min, max, value = _get_min_max_value(None, None, o)
         return IntSliderWidget(value=o, min=min, max=max)
+
+def _widget_abbrev(o):
+    """Make widgets from abbreviations: single values, lists or tuples."""
     if isinstance(o, (list, tuple)):
         if _matches(o, (int, int)):
             min, max, value = _get_min_max_value(o[0], o[1], None)
             return IntSliderWidget(value=value, min=min, max=max)
         elif _matches(o, (int, int, int)):
             min, max, value = _get_min_max_value(o[0], o[1], None)
             return IntSliderWidget(value=value, min=min, max=max, step=o[2])
         elif _matches(o, (float, float)):
             min, max, value = _get_min_max_value(o[0], o[1], None)
             return FloatSliderWidget(value=value, min=min, max=max)
         elif _matches(o, (float, float, float)):
             min, max, value = _get_min_max_value(o[0], o[1], None)
             return FloatSliderWidget(value=value, min=min, max=max, step=o[2])
         elif _matches(o, (float, float, int)):
             min, max, value = _get_min_max_value(o[0], o[1], None)
             return FloatSliderWidget(value=value, min=min, max=max, step=float(o[2]))
         elif all(isinstance(x, string_types) for x in o):
             return DropdownWidget(value=unicode_type(o[0]),
                                    values=[unicode_type(k) for k in o])
 
+    else:
+        return _widget_abbrev_single_value(o)
+
+def _widget_or_abbrev(value):
+    if isinstance(value, Widget):
+        return value
+    
+    widget = _widget_abbrev(value)
+    if widget is None:
+        raise ValueError("%r cannot be transformed to a Widget" % value)
+    return widget
+
+def _widget_for_param(param, kwargs):
+    """Get a widget for a parameter.
+    
+    We look for, in this order:
+    - keyword arguments passed to interact[ive]() that match the parameter name.
+    - function annotations
+    - default values
+    
+    Returns an instance of Widget, or None if nothing suitable is found.
+    
+    Raises ValueError if the kwargs or annotation value cannot be made into
+    a widget.
+    """
+    if param.name in kwargs:
+        return _widget_or_abbrev(kwargs.pop(param.name))
+    
+    if param.annotation is not Parameter.empty:
+        return _widget_or_abbrev(param.annotation)
+    
+    if param.default is not Parameter.empty:
+        # Returns None if it's not suitable
+        return _widget_abbrev_single_value(param.default)
+    
+    return None
 
 def interactive(f, **kwargs):
-    """Interact with a function using widgets."""
+    """Build a group of widgets for setting the inputs to a function."""
     
     co = kwargs.pop('clear_output', True)
     # First convert all args to Widget instances
     widgets = []
     container = ContainerWidget()
     container.result = None
     container.kwargs = dict()
-    for key, value in kwargs.items():
-        if isinstance(value, Widget):
-            widget = value
-        else:
-            widget = _widget_abbrev(value)
-            if widget is None:
-                raise ValueError("Object cannot be transformed to a Widget")
-        widget.description = key
-        widgets.append((key,widget))
-    widgets.sort(key=lambda e: e[1].__class__.__name__)
-    container.children = [e[1] for e in widgets]
+    
+    # Extract parameters from the function signature
+    for param in signature(f).parameters.values():
+        param_widget = _widget_for_param(param, kwargs)
+        if param_widget is not None:
+            param_widget.description = param.name
+            widgets.append(param_widget)
+    
+    # Extra parameters from keyword args - we assume f takes **kwargs
+    for name, value in sorted(kwargs.items(), key = lambda x: x[0]):
+        widget = _widget_or_abbrev(value)
+        widget.description = name
+        widgets.append(widget)
+    
+    # This has to be done as an assignment, not using container.children.append,
+    # so that traitlets notices the update.
+    container.children = widgets
 
     # Build the callback
     def call_f(name, old, new):
         actual_kwargs = {}
-        for key, widget in widgets:
+        for widget in widgets:
             value = widget.value
-            container.kwargs[key] = value
-            actual_kwargs[key] = value
+            container.kwargs[widget.description] = value
+            actual_kwargs[widget.description] = value
         if co:
             clear_output(wait=True)
         container.result = f(**actual_kwargs)
 
     # Wire up the widgets
-    for key, widget in widgets:
+    for widget in widgets:
         widget.on_trait_change(call_f, 'value')
 
     container.on_displayed(lambda _: call_f(None, None, None))
 
     return container
 
 def interact(f, **kwargs):
+    """Interact with a function using widgets."""
     w = interactive(f, **kwargs)
     f.widget = w
     display(w)