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bpo-40397: Fix subscription of nested generic alias without parameters. #20021

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Merged
merged 1 commit into from
May 10, 2020
Merged

bpo-40397: Fix subscription of nested generic alias without parameters. #20021

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13 changes: 12 additions & 1 deletion Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@
from typing import TypeVar, AnyStr
from typing import T, KT, VT # Not in __all__.
from typing import Union, Optional, Literal
from typing import Tuple, List, MutableMapping
from typing import Tuple, List, Dict, MutableMapping
from typing import Callable
from typing import Generic, ClassVar, Final, final, Protocol
from typing import cast, runtime_checkable
Expand Down Expand Up @@ -3173,6 +3173,17 @@ def test_frozenset(self):
def test_dict(self):
self.assertIsSubclass(dict, typing.Dict)

def test_dict_subscribe(self):
K = TypeVar('K')
V = TypeVar('V')
self.assertEqual(Dict[K, V][str, int], Dict[str, int])
self.assertEqual(Dict[K, int][str], Dict[str, int])
self.assertEqual(Dict[str, V][int], Dict[str, int])
self.assertEqual(Dict[K, List[V]][str, int], Dict[str, List[int]])
self.assertEqual(Dict[K, List[int]][str], Dict[str, List[int]])
self.assertEqual(Dict[K, list[V]][str, int], Dict[str, list[int]])
self.assertEqual(Dict[K, list[int]][str], Dict[str, list[int]])

def test_no_list_instantiation(self):
with self.assertRaises(TypeError):
typing.List()
Expand Down
6 changes: 4 additions & 2 deletions Lib/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -702,8 +702,10 @@ def __getitem__(self, params):
if isinstance(arg, TypeVar):
arg = subst[arg]
elif isinstance(arg, (_GenericAlias, GenericAlias)):
subargs = tuple(subst[x] for x in arg.__parameters__)
arg = arg[subargs]
subparams = arg.__parameters__
if subparams:
subargs = tuple(subst[x] for x in subparams)
arg = arg[subargs]
new_args.append(arg)
return self.copy_with(tuple(new_args))

Expand Down