[jira] [Created] (ARROW-17018) Timedelta dtype metadata base unit is globally mutated by the Table.to_pandas() method

["Phillip Cloud (Jira)" <ji...@apache.org>]

Phillip Cloud created ARROW-17018:
-------------------------------------

             Summary: Timedelta dtype metadata base unit is globally mutated by the Table.to_pandas() method
                 Key: ARROW-17018
                 URL: https://issues.apache.org/jira/browse/ARROW-17018
             Project: Apache Arrow
          Issue Type: Bug
          Components: C++, Python
    Affects Versions: 8.0.0
            Reporter: Phillip Cloud
             Fix For: 9.0.0


Here's a failing test case to demonstrate the issue:

{code}
def test_mutates_dtype():
    import pyarrow as pa

    expected = np.dtype('<m8')

    assert np.dtype(np.timedelta64) == expected

    df = pd.DataFrame({"a": [np.timedelta64()]})
    t = pa.Table.from_pandas(df)
    t.to_pandas()

    assert np.dtype(np.timedelta64) == expected
{code}



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