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bpo-45679: Do not cache typing.Literal with more than one type arg #29333

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bpo-45679: Do not cache typing.Literal with more than one type arg #29333

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18 changes: 18 additions & 0 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3298,6 +3298,24 @@ def test_top_level_class_var(self):
):
get_type_hints(ann_module6)

def test_hints_with_literal_cache(self):
# https://bugs.python.org/issue45679
Literal[True] # to trigger cache
def func(arg: Literal[1]):
pass

hints = get_type_hints(func)
# We use such complex way of comparing things, because `1 == True`
self.assertEqual(str(hints['arg']), "typing.Literal[1]")

# Two args case, which was causing an issue:
Literal[1, 'a']
def func(arg: Literal[True, 'a']):
pass

hints = get_type_hints(func)
self.assertEqual(str(hints['arg']), "typing.Literal[True, 'a']")


class GetUtilitiesTestCase(TestCase):
def test_get_origin(self):
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12 changes: 8 additions & 4 deletions Lib/typing.py
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Expand Up @@ -312,10 +312,14 @@ def decorator(func):

@functools.wraps(func)
def inner(*args, **kwds):
try:
return cached(*args, **kwds)
except TypeError:
pass # All real errors (not unhashable args) are raised below.
# We call `cached`, only if we don't care about types,
# or when we have just a single argument. Otherwise we can confuse
# `Literal[1, 'a']` with `Literal[True, 'a']`, see: bpo-45679
if not typed or len(args) <= 1:
try:
return cached(*args, **kwds)
except TypeError:
pass # All real errors (not unhashable args) are raised below.
return func(*args, **kwds)
return inner

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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2021-10-30-20-27-59.bpo-45679.gwXa77.rst
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@@ -0,0 +1,2 @@
Do not cache :class:`typing.Literal` when it has more than one type
argument.