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BUG: Fix unpickling of string dtypes of legacy pandas versions #61770

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BUG: Fix unpickling of string dtypes of legacy pandas versions #61770

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7eec271
Fix StringDtype compat with old pickles
Liam3851 Jul 3, 2025
cbf1eae
Add pandas string dtypes to legacy pickle tests.
Liam3851 Jul 3, 2025
184e55c
Remove stray diff.
Liam3851 Jul 3, 2025
3b8e6ae
Fix formatting.
Liam3851 Jul 3, 2025
430dd44
Add type hint to setstate.
Liam3851 Jul 3, 2025
3d612b2
Import MutableMapping
Liam3851 Jul 3, 2025
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6 changes: 6 additions & 0 deletions pandas/core/arrays/string_.py
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Original file line number Diff line number Diff line change
Expand Up @@ -72,6 +72,8 @@
from pandas.io.formats import printing

if TYPE_CHECKING:
from collections.abc import MutableMapping

import pyarrow

from pandas._typing import (
Expand Down Expand Up @@ -218,6 +220,10 @@ def __eq__(self, other: object) -> bool:
return self.storage == other.storage and self.na_value is other.na_value
return False

def __setstate__(self, state: MutableMapping[str, Any]) -> None:
self.storage = state.pop("storage", "python")
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Suggested change
self.storage = state.pop("storage", "python")
# back-compat for pandas < 2.3, where na_value did not yet exist
self.storage = state.pop("storage", "python")

self._na_value = state.pop("_na_value", libmissing.NA)

def __hash__(self) -> int:
# need to override __hash__ as well because of overriding __eq__
return super().__hash__()
Expand Down
Binary file added pandas/tests/io/data/legacy_pickle/1.5.3/1.5.3_x86_64_win_3.11.13.pickle
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8 changes: 8 additions & 0 deletions pandas/tests/io/generate_legacy_storage_files.py
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Expand Up @@ -147,6 +147,7 @@ def create_pickle_data():
"float": Index(np.arange(10, dtype=np.float64)),
"uint": Index(np.arange(10, dtype=np.uint64)),
"timedelta": timedelta_range("00:00:00", freq="30min", periods=10),
"string": Index(["foo", "bar", "baz", "qux", "quux"], dtype="string"),
}

index["range"] = RangeIndex(10)
Expand Down Expand Up @@ -185,6 +186,7 @@ def create_pickle_data():
"dt": Series(date_range("20130101", periods=5)),
"dt_tz": Series(date_range("20130101", periods=5, tz="US/Eastern")),
"period": Series([Period("2000Q1")] * 5),
"string": Series(["foo", "bar", "baz", "qux", "quux"], dtype="string"),
}

mixed_dup_df = DataFrame(data)
Expand Down Expand Up @@ -233,6 +235,12 @@ def create_pickle_data():
},
index=range(5),
),
"string": DataFrame(
{
"A": Series(["foo", "bar", "baz", "qux", "quux"], dtype="string"),
"B": Series(["one", "two", "one", "two", "three"], dtype="string"),
}
),
}

cat = {
Expand Down
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