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

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Merged
vstinner merged 4 commits into from
Feb 21, 2026
Merged

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

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4052dd2
gh-141510: Fix copy.deepcopy() for recursive frozendict
vstinner Feb 19, 2026
046e917
Add more tests
vstinner Feb 20, 2026
52d7c83
Merge branch 'main' into frozendict_deepcopy
vstinner Feb 21, 2026
2a46195
Add more tests
vstinner Feb 21, 2026
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12 changes: 11 additions & 1 deletion 12 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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17 changes: 17 additions & 0 deletions 17 Lib/test/test_copy.py
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Expand Up @@ -432,6 +432,23 @@ 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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y = copy.deepcopy(x)
self.assertEqual(y.keys(), x.keys())
self.assertIsNot(x, y)
self.assertIsNot(x["foo"], y["foo"])
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self.assertIs(y['foo'][0], y)

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

@serhiy-storchaka serhiy-storchaka Feb 21, 2026

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Add also other assertions similar to the above ones:

        self.assertEqual(y, x)
        self.assertIsNot(x, y)
        self.assertIsNot(x[0], y[0])

@vstinner vstinner Feb 21, 2026

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self.assertEqual(y, x) fails with RecursionError. I added the two other tests.


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