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gh-141510: Fix copy.deepcopy() for recursive frozendict #145027

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gh-141510: Fix copy.deepcopy() for recursive frozendict #145027

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12 changes: 11 additions & 1 deletion Lib/copy.py
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Original file line number Diff line number Diff line change
Expand Up @@ -204,7 +204,17 @@ def _deepcopy_dict(x, memo, deepcopy=deepcopy):
d[dict] = _deepcopy_dict

def _deepcopy_frozendict(x, memo, deepcopy=deepcopy):
y = _deepcopy_dict(x, memo, deepcopy)
y = {}
for key, value in x.items():
y[deepcopy(key, memo)] = deepcopy(value, memo)

# We're not going to put the frozendict in the memo, but it's still
# important we check for it, in case the frozendict contains recursive
# mutable structures.
try:
return memo[id(x)]
except KeyError:
pass
return frozendict(y)
d[frozendict] = _deepcopy_frozendict

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8 changes: 8 additions & 0 deletions Lib/test/test_copy.py
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Expand Up @@ -432,6 +432,14 @@ def test_deepcopy_frozendict(self):
self.assertIsNot(x, y)
self.assertIsNot(x["foo"], y["foo"])

# recursive frozendict
x = frozendict(foo=[])
x['foo'].append(x)
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@serhiy-storchaka serhiy-storchaka Feb 20, 2026

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Test also a list containing a frozendict.

x = frozendict(foo=[])
x['foo'].append(x)
x = x['foo']
...
self.assertIs(y[0]['foo'], y)

y = copy.deepcopy(x)
self.assertEqual(y.keys(), x.keys())
self.assertIsNot(x, y)
self.assertIsNot(x["foo"], y["foo"])
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@serhiy-storchaka serhiy-storchaka Feb 20, 2026

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Add the recursion test:

self.assertIs(y['foo'][0], y)


@support.skip_emscripten_stack_overflow()
@support.skip_wasi_stack_overflow()
def test_deepcopy_reflexive_dict(self):
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