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import typing
from typish.classes._subscriptable_type import SubscriptableType
def is_literal_type(cls: typing.Any) -> bool:
"""
Return whether cls is a Literal type.
:param cls: the type that is to be checked.
:return: True if cls is a Literal type.
"""
from typish.functions._get_simple_name import get_simple_name
return get_simple_name(cls) == 'Literal'
class _LiteralMeta(SubscriptableType):
"""
A Metaclass that exists to serve Literal and alter the __args__ attribute.
"""
def __getattribute__(cls, item):
"""
This method makes sure that __args__ is a tuple, like with
typing.Literal.
:param item: the name of the attribute that is obtained.
:return: the attribute.
"""
if item == '__args__':
try:
result = SubscriptableType.__getattribute__(cls, item)
if (result and isinstance(result, tuple)
and isinstance(result[0], tuple)):
result = result[0] # result was a tuple in a tuple.
if result and not isinstance(result, tuple):
result = (result,)
except AttributeError: # pragma: no cover
# In case of Python 3.5
result = tuple()
elif item in ('__origin__', '__name__', '_name'):
result = 'Literal'
else:
result = SubscriptableType.__getattribute__(cls, item)
return result
def __instancecheck__(self, instance):
return self.__args__ and instance in self.__args__
def __str__(self):
args = ', '.join(str(arg) for arg in self.__args__)
return '{}[{}]'.format(self.__name__, args)
def __subclasscheck__(self, subclass: typing.Any) -> bool:
return is_literal_type(subclass)
class LiteralAlias(type, metaclass=_LiteralMeta):
"""
This is a backwards compatible variant of typing.Literal (Python 3.8+).
"""
@staticmethod
def from_literal(literal: typing.Any) -> typing.Type['LiteralAlias']:
"""
Create a LiteralAlias from the given typing.Literal.
:param literal: the typing.Literal type.
:return: a LiteralAlias type.
"""
from typish.functions._get_args import get_args
args = get_args(literal)
return LiteralAlias[args] if args else LiteralAlias
# If Literal is available (Python 3.8+), then return that type instead.
Literal = getattr(typing, 'Literal', LiteralAlias)
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