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TST: DataFrame.update preserves mixed dtypes #63163

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TST: DataFrame.update preserves mixed dtypes #63163

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2bfbc69
Test added for preserve mixed dtypes on update
jfegg Nov 20, 2025
d1a92fa
Merge branch 'pandas-dev:main' into main
jfegg Nov 20, 2025
5618104
Fixed namespace issue
jfegg Nov 20, 2025
18c2b53
Add Int64 test to original update test
jfegg Nov 20, 2025
52dabdd
Merge branch 'main' into main
jfegg Nov 20, 2025
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17 changes: 17 additions & 0 deletions pandas/tests/frame/methods/test_update.py
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Original file line number Diff line number Diff line change
Expand Up @@ -197,6 +197,7 @@ def test_update_dt_column_with_NaT_create_column(self):
np.datetime64("2000-01-02T00:00:00"),
np.dtype("datetime64[ns]"),
),
(1, 2, pd.Int64Dtype()),
],
)
def test_update_preserve_dtype(self, value_df, value_other, dtype):
Expand Down Expand Up @@ -228,3 +229,19 @@ def test_update_on_duplicate_frame_unique_argument_index(self):
expected = DataFrame({"a": [2, 2, 3]}, index=[1, 1, 2], dtype=np.dtype("intc"))
df.update(other)
tm.assert_frame_equal(df, expected)

def test_update_preserve_mixed_dtypes(self):
# GH#44104
dtype1 = pd.Int64Dtype()
dtype2 = pd.StringDtype()
df = DataFrame({"a": [1, 2, 3], "b": ["x", "y", "z"]})
df = df.astype({"a": dtype1, "b": dtype2})

other = DataFrame({"a": [4, 5], "b": ["a", "b"]})
other = other.astype({"a": dtype1, "b": dtype2})

expected = DataFrame({"a": [4, 5, 3], "b": ["a", "b", "z"]})
expected = expected.astype({"a": dtype1, "b": dtype2})

df.update(other)
tm.assert_frame_equal(df, expected)
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