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gh-105509: Simplify implementation of typing.Annotated (#105510)

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Alex Waygood 2023-09-01 21:57:25 +01:00 • committed by GitHub
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commit a1cbace91b
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3 changed files with 17 additions and 27 deletions
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38
Lib/typing.py
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@ -2001,7 +2001,8 @@ class _AnnotatedAlias(_NotIterable, _GenericAlias, _root=True):
return (self.__origin__,)
class Annotated:
@_SpecialForm
def Annotated(self, params):
"""Add context-specific metadata to a type.
Example: Annotated[int, runtime_check.Unsigned] indicates to the
@ -2048,30 +2049,17 @@ class Annotated:
where T1, T2 etc. are TypeVars, which would be invalid, because
only one type should be passed to Annotated.
"""
__slots__ = ()
def __new__(cls, *args, **kwargs):
raise TypeError("Type Annotated cannot be instantiated.")
@_tp_cache
def __class_getitem__(cls, params):
if not isinstance(params, tuple) or len(params) < 2:
raise TypeError("Annotated[...] should be used "
"with at least two arguments (a type and an "
"annotation).")
if _is_unpacked_typevartuple(params[0]):
raise TypeError("Annotated[...] should not be used with an "
"unpacked TypeVarTuple")
msg = "Annotated[t, ...]: t must be a type."
origin = _type_check(params[0], msg, allow_special_forms=True)
metadata = tuple(params[1:])
return _AnnotatedAlias(origin, metadata)
def __init_subclass__(cls, *args, **kwargs):
raise TypeError(
"Cannot subclass {}.Annotated".format(cls.__module__)
)
if not isinstance(params, tuple) or len(params) < 2:
raise TypeError("Annotated[...] should be used "
"with at least two arguments (a type and an "
"annotation).")
if _is_unpacked_typevartuple(params[0]):
raise TypeError("Annotated[...] should not be used with an "
"unpacked TypeVarTuple")
msg = "Annotated[t, ...]: t must be a type."
origin = _type_check(params[0], msg, allow_special_forms=True)
metadata = tuple(params[1:])
return _AnnotatedAlias(origin, metadata)
def runtime_checkable(cls):