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BUG: Fix to_datetime not respecting dayfirst #58876

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Merged
merged 6 commits into from
Jul 17, 2024
Merged

BUG: Fix to_datetime not respecting dayfirst #58876

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e90bb56
ENH: Warn when to_datetime falls back to dateutil when dayfirst is pa…
Aloqeely Jun 1, 2024
82ac17b
Assert warnings
Aloqeely Jun 1, 2024
ed523ef
Remove warnings and fix functionality
Aloqeely Jul 4, 2024
6b51d28
Merge branch 'main' into warn-to_datetime-fails-guess-dayfirst
Aloqeely Jul 4, 2024
4c27530
Add whatsnew, write test
Aloqeely Jul 7, 2024
14286bb
Merge branch 'main' into warn-to_datetime-fails-guess-dayfirst
Aloqeely Jul 16, 2024
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5 changes: 3 additions & 2 deletions pandas/core/tools/datetimes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -135,10 +135,11 @@ def _guess_datetime_format_for_array(arr, dayfirst: bool | None = False) -> str
return guessed_format
# If there are multiple non-null elements, warn about
# how parsing might not be consistent
if tslib.first_non_null(arr[first_non_null + 1 :]) != -1:
if dayfirst or tslib.first_non_null(arr[first_non_null + 1 :]) != -1:
warnings.warn(
"Could not infer format, so each element will be parsed "
"individually, falling back to `dateutil`. To ensure parsing is "
"individually, falling back to `dateutil` which does not take the "
"dayfirst parameter in consideration. To ensure parsing is "
"consistent and as-expected, please specify a format.",
UserWarning,
stacklevel=find_stack_level(),
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8 changes: 5 additions & 3 deletions pandas/tests/tools/test_to_datetime.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3007,9 +3007,11 @@ def test_parsers_dayfirst_yearfirst(
result2 = Timestamp(date_str)
assert result2 == expected

result3 = to_datetime(
date_str, dayfirst=dayfirst, yearfirst=yearfirst, cache=cache
)
warn = UserWarning if dayfirst else None
with tm.assert_produces_warning(warn, match="Could not infer format"):
result3 = to_datetime(
date_str, dayfirst=dayfirst, yearfirst=yearfirst, cache=cache
)

result4 = DatetimeIndex([date_str], dayfirst=dayfirst, yearfirst=yearfirst)[0]

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