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"""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 2.7 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,
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):
if cls is type:
meth = getattr(cls, method_name)
for name in nested:
meth = getattr(meth, name, meth)
except AttributeError:
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):
if obj.__self__ is None:
# Unbound method - treat it as a function (no distinction in Py 3)
obj = obj.__func__
# Bound method: trim off the first parameter (typically self or cls)
sig = signature(obj.__func__)
return sig.replace(parameters=tuple(sig.parameters.values())[1:])
sig = obj.__signature__
except AttributeError:
if sig is not None:
return sig
# Was this function wrapped by a decorator?
wrapped = obj.__wrapped__
except AttributeError:
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 {}
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,
elif (param.kind not in (_VAR_KEYWORD, _VAR_POSITIONAL) and
not param._partial_kwarg):
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)
# 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)
# 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):
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')
_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.KEYWORD_ONLY`, `Parameter.VAR_KEYWORD`.
__slots__ = ('_name', '_kind', '_default', '_annotation', '_partial_kwarg')
empty = _empty
def __init__(self, name, kind, default=_empty, annotation=_empty,
raise ValueError("invalid value for 'Parameter.kind' attribute")
self._kind = kind
if default is not _empty:
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
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
def name(self):
return self._name
def default(self):
return self._default
def annotation(self):
return self._annotation
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,
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,
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 :meth:`Signature.bind` call. Holds the mapping of arguments
to the function's parameters.
Has the following public attributes:
arguments : :class:`collections.OrderedDict`
An ordered mutable mapping of parameters' names to arguments' values.
Does not contain arguments' default values.
signature : :class:`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
def signature(self):
return self._signature
def args(self):
args = []
for param_name, param in self._signature.parameters.items():
if (param.kind in (_VAR_KEYWORD, _KEYWORD_ONLY) or
# Keyword arguments mapped by 'functools.partial'
# (Parameter._partial_kwarg is True) are mapped
# in 'BoundArguments.kwargs', along with VAR_KEYWORD &
arg = self.arguments[param_name]
except KeyError:
# We're done here. Other arguments
# will be mapped in 'BoundArguments.kwargs'
if param.kind == _VAR_POSITIONAL:
# *args
# plain argument
return tuple(args)
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
kwargs_started = True
if param_name not in self.arguments:
kwargs_started = True
if not kwargs_started:
arg = self.arguments[param_name]
except KeyError:
if param.kind == _VAR_KEYWORD:
# **kwargs
# 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:
parameters : :class:`collections.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`).
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.
__slots__ = ('_return_annotation', '_parameters')
_parameter_cls = Parameter
_bound_arguments_cls = BoundArguments
empty = _empty
def __init__(self, parameters=None, return_annotation=_empty,
'''Constructs Signature from the given list of Parameter
objects and 'return_annotation'. All arguments are optional.
if parameters is None:
params = OrderedDict()
if __validate_parameters__:
params = OrderedDict()
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)
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
params = OrderedDict(((param.name, param)
for param in parameters))
self._parameters = params
self._return_annotation = return_annotation
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)
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,
# ... w/ defaults.
for offset, name in enumerate(positional[non_default_count:]):
annotation = annotations.get(name, _empty)
parameters.append(Parameter(name, annotation=annotation,
# *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,
# 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,
# **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,
return cls(parameters,
return_annotation=annotations.get('return', _empty),
def parameters(self):
return types.MappingProxyType(self._parameters)
except AttributeError:
return OrderedDict(self._parameters.items())
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,
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:
other_param = other.parameters[param_name]
except KeyError:
return False
if param != other_param:
return False
other_idx = other_positions[param_name]
except KeyError:
return False
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
arg_val = next(arg_vals)
except StopIteration:
# No more positional arguments
param = next(parameters)
except StopIteration:
# No more parameters. That's it. Just need to check that
# we have no `kwargs` after this while loop
if param.kind == _VAR_POSITIONAL:
# That's OK, just empty *args. Let's start parsing
# kwargs
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,)
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,)
if partial:
parameters_ex = (param,)
msg = '{arg!r} parameter lacking default value'
msg = msg.format(arg=param.name)
raise TypeError(msg)
# We have a positional argument to process
param = next(parameters)
except StopIteration:
raise TypeError('too many positional arguments')
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]
arguments[param.name] = tuple(values)
if param.name in kwargs:
raise TypeError('multiple values for argument '
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'. \
if param.kind == _VAR_KEYWORD:
# Memorize that we have a '**kwargs'-like parameter
kwargs_param = param
param_name = param.name
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'. \
arguments[param_name] = arg_val
if kwargs:
if kwargs_param is not None:
# Process our '**kwargs'-like parameter
arguments[kwargs_param.name] = kwargs
raise TypeError('too many keyword arguments')
return self._bound_arguments_cls(self, arguments)
def bind(self, *args, **kwargs):
'''Get a :class:`BoundArguments` object, that maps the passed `args`
and `kwargs` to the function's signature. Raises :exc:`TypeError`
if the passed arguments can not be bound.
return self._bind(args, kwargs)
def bind_partial(self, *args, **kwargs):
'''Get a :class:`BoundArguments` object, that partially maps the
passed `args` and `kwargs` to the function's signature.
Raises :exc:`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)
# This condition should be only triggered once, so
# reset the flag
render_kw_only_separator = False
rendered = '({0})'.format(', '.join(result))
if self.return_annotation is not _empty:
anno = formatannotation(self.return_annotation)
rendered += ' -> {0}'.format(anno)
return rendered