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BUG GH#43414 Infer and coerce datetimes am pm #43416

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BUG GH#43414 Infer and coerce datetimes am pm #43416

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aa6c02a
TST GH#43414 Add tests for to infer and coerce datetime with am / pm.
Sep 5, 2021
384f44b
BUG GH#43414 Add am/pm logic to guess_datetime_format.
Sep 5, 2021
ec55349
Merge branch 'master' into infer-datetimes-am-pm
Sep 7, 2021
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7 changes: 7 additions & 0 deletions pandas/_libs/tslibs/parsing.pyx
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Original file line number Diff line number Diff line change
Expand Up @@ -892,6 +892,8 @@ def guess_datetime_format(
if not isinstance(dt_str, str):
return None

valid_am_pm = ['am', 'pm', 'a', 'p']

day_attribute_and_format = (('day',), '%d', 2)

# attr name, format, padding (if any)
Expand Down Expand Up @@ -947,6 +949,11 @@ def guess_datetime_format(
found_attrs.update(attrs)
break

# Final formatting is required if the dt_string contains AM/PM.
if tokens[i].lower() in valid_am_pm:
format_guess = ["%I" if guess == "%H" else guess for guess in format_guess]
format_guess[i] = "%p"

# Only consider it a valid guess if we have a year, month and day
if len({'year', 'month', 'day'} & found_attrs) != 3:
return None
Expand Down
35 changes: 35 additions & 0 deletions pandas/tests/tools/test_to_datetime.py
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Expand Up @@ -1965,6 +1965,41 @@ def test_to_datetime_infer_datetime_format_consistent_format(self, cache):
tm.assert_series_equal(with_format, no_infer)
tm.assert_series_equal(no_infer, yes_infer)

@pytest.mark.parametrize("cache", [True, False])
@pytest.mark.parametrize("errors", ["ignore", "coerce", "raise"])
def test_to_datetime_infer_datetime_consistent_formats_error_types(
self, cache, errors
):
# GH#43414
s = Series(date_range("20000101", periods=50, freq="H"))
begin_timerange_condition = s.dt.hour >= 7
end_timerange_condition = s.dt.hour <= 13
s = s.loc[begin_timerange_condition & end_timerange_condition]

test_formats = [
"%m-%d-%Y",
"%m/%d/%Y %H:%M:%S.%f",
"%m/%d/%Y %I:%M:%S%p",
"%m/%d/%Y %I:%M:%S %p",
"%Y-%m-%dT%H:%M:%S.%f",
"%Y-%m-%dT%I:%M:%S%p",
"%Y-%m-%dT%I:%M:%S %p",
"%Y-%m-%d %H:%M:%S.%f",
"%Y-%m-%d %I:%M:%S%p",
"%Y-%m-%d %I:%M:%S %p",
]

for test_format in test_formats:
s_as_dt_strings = s.apply(lambda x: x.strftime(test_format))

explicit_format = to_datetime(
s_as_dt_strings, errors=errors, format=test_format, cache=cache
)
inferred_format = to_datetime(
s_as_dt_strings, errors=errors, infer_datetime_format=True, cache=cache
)
tm.assert_series_equal(explicit_format, inferred_format)

@pytest.mark.parametrize("cache", [True, False])
def test_to_datetime_infer_datetime_format_inconsistent_format(self, cache):
s = Series(
Expand Down