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"""Defines experimental extensions to the standard "typing" module that are
supported by the mypy typechecker.
Example usage:
from mypy_extensions import TypedDict
from typing import Any
# NOTE: This module must support Python 2.7 in addition to Python 3.x
import sys
# _type_check is NOT a part of public typing API, it is used here only to mimic
# the (convenient) behavior of types provided by typing module.
from typing import _type_check # type: ignore
def _check_fails(cls, other):
if sys._getframe(1).f_globals['__name__'] not in ['abc', 'functools', 'typing']:
# Typed dicts are only for static structural subtyping.
raise TypeError('TypedDict does not support instance and class checks')
except (AttributeError, ValueError):
return False
def _dict_new(cls, *args, **kwargs):
return dict(*args, **kwargs)
def _typeddict_new(cls, _typename, _fields=None, **kwargs):
total = kwargs.pop('total', True)
if _fields is None:
_fields = kwargs
elif kwargs:
raise TypeError("TypedDict takes either a dict or keyword arguments,"
" but not both")
ns = {'__annotations__': dict(_fields), '__total__': total}
# Setting correct module is necessary to make typed dict classes pickleable.
ns['__module__'] = sys._getframe(1).f_globals.get('__name__', '__main__')
except (AttributeError, ValueError):
return _TypedDictMeta(_typename, (), ns)
class _TypedDictMeta(type):
def __new__(cls, name, bases, ns, total=True):
# Create new typed dict class object.
# This method is called directly when TypedDict is subclassed,
# or via _typeddict_new when TypedDict is instantiated. This way
# TypedDict supports all three syntaxes described in its docstring.
# Subclasses and instances of TypedDict return actual dictionaries
# via _dict_new.
ns['__new__'] = _typeddict_new if name == 'TypedDict' else _dict_new
tp_dict = super(_TypedDictMeta, cls).__new__(cls, name, (dict,), ns)
anns = ns.get('__annotations__', {})
msg = "TypedDict('Name', {f0: t0, f1: t1, ...}); each t must be a type"
anns = {n: _type_check(tp, msg) for n, tp in anns.items()}
for base in bases:
anns.update(base.__dict__.get('__annotations__', {}))
tp_dict.__annotations__ = anns
if not hasattr(tp_dict, '__total__'):
tp_dict.__total__ = total
return tp_dict
__instancecheck__ = __subclasscheck__ = _check_fails
TypedDict = _TypedDictMeta('TypedDict', (dict,), {})
TypedDict.__module__ = __name__
TypedDict.__doc__ = \
"""A simple typed name space. At runtime it is equivalent to a plain dict.
TypedDict creates a dictionary type that expects all of its
instances to have a certain set of keys, with each key
associated with a value of a consistent type. This expectation
is not checked at runtime but is only enforced by typecheckers.
Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'label': str})
a: Point2D = {'x': 1, 'y': 2, 'label': 'good'} # OK
b: Point2D = {'z': 3, 'label': 'bad'} # Fails type check
assert Point2D(x=1, y=2, label='first') == dict(x=1, y=2, label='first')
The type info could be accessed via Point2D.__annotations__. TypedDict
supports two additional equivalent forms::
Point2D = TypedDict('Point2D', x=int, y=int, label=str)
class Point2D(TypedDict):
x: int
y: int
label: str
The latter syntax is only supported in Python 3.6+, while two other
syntax forms work for Python 2.7 and 3.2+
# Argument constructors for making more-detailed Callables. These all just
# return their type argument, to make them complete noops in terms of the
# `typing` module.
def Arg(type=Any, name=None):
"""A normal positional argument"""
return type
def DefaultArg(type=Any, name=None):
"""A positional argument with a default value"""
return type
def NamedArg(type=Any, name=None):
"""A keyword-only argument"""
return type
def DefaultNamedArg(type=Any, name=None):
"""A keyword-only argument with a default value"""
return type
def VarArg(type=Any):
"""A *args-style variadic positional argument"""
return type
def KwArg(type=Any):
"""A **kwargs-style variadic keyword argument"""
return type
# Return type that indicates a function does not return
class NoReturn: pass
def trait(cls):
return cls
def mypyc_attr(*attrs, **kwattrs):
return lambda x: x
# TODO: We may want to try to properly apply this to any type
# variables left over...
class _FlexibleAliasClsApplied:
def __init__(self, val):
self.val = val
def __getitem__(self, args):
return self.val
class _FlexibleAliasCls:
def __getitem__(self, args):
return _FlexibleAliasClsApplied(args[-1])
FlexibleAlias = _FlexibleAliasCls()