BUG: Fix inconsistent datetime types between calamine and openpyxl readers (#59186) #63318
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…aders (pandas-dev#59186) The calamine Excel reader was returning pd.Timestamp and pd.Timedelta for datetime values in mixed-type columns, while openpyxl returns standard library datetime.datetime and datetime.timedelta objects. This change modifies the calamine reader to return standard library datetime types, ensuring consistent behavior across Excel reader engines. - Return datetime.datetime as-is instead of converting to pd.Timestamp - Convert date objects to datetime to match openpyxl behavior - Return datetime.timedelta as-is instead of converting to pd.Timedelta - Remove unused pandas import - Update test helper get_exp_unit() to reflect new consistent behavior
mroeschke
requested changes
Dec 10, 2025
pandas/io/excel/_calamine.py
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| elif isinstance(value, timedelta): | ||
| return pd.Timedelta(value) | ||
| # Return datetime.timedelta as-is to match openpyxl behavior (GH#59186) | ||
| # (previously returned pd.Timedelta) | ||
| return value |
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Can you combine this branch with the isinstance(value, datetime) branch by combining the isinstance checks?
mroeschke
approved these changes
Dec 11, 2025
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Thanks @yjennyli |
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closes #59186
When reading Excel files with mixed data types (strings, dates, numbers in the same column), the calamine and openpyxl engines returned different Python types for datetime values:
datetime.datetimepd.TimestampThis is confusing for users who expect consistent behavior regardless of which engine they use.
This PR Changes the calamine reader to return standard library types (
datetime.datetime,datetime.timedelta) instead of pandas types (pd.Timestamp,pd.Timedelta), matching openpyxl's behavior.Testing:
All existing Excel reader tests pass (1467 passed)
Manual testing confirms both engines now return the same types