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BUG: CustomBusinessMonthBegin(End) sometimes ignores extra offset (GH41356) #41488

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Jul 28, 2021
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v1.4.0.rst
Original file line number Diff line number Diff line change
Expand Up @@ -281,6 +281,7 @@ Styler

Other
^^^^^
- Bug in :meth:`CustomBusinessMonthBegin.__add__` (:meth:`CustomBusinessMonthEnd.__add__`) not applying the extra ``offset`` parameter when beginning (end) of the target month is already a business day (:issue:`41356`)

.. ***DO NOT USE THIS SECTION***

Expand Down
8 changes: 7 additions & 1 deletion pandas/_libs/tslibs/offsets.pyx
Original file line number Diff line number Diff line change
Expand Up @@ -3370,7 +3370,10 @@ cdef class _CustomBusinessMonth(BusinessMixin):
"""
Define default roll function to be called in apply method.
"""
cbday = CustomBusinessDay(n=self.n, normalize=False, **self.kwds)
cbday_kwds = self.kwds.copy()
cbday_kwds['offset'] = timedelta(0)

cbday = CustomBusinessDay(n=1, normalize=False, **cbday_kwds)

if self._prefix.endswith("S"):
# MonthBegin
Expand Down Expand Up @@ -3414,6 +3417,9 @@ cdef class _CustomBusinessMonth(BusinessMixin):

new = cur_month_offset_date + n * self.m_offset
result = self.cbday_roll(new)

if self.offset:
result = result + self.offset
return result


Expand Down
105 changes: 105 additions & 0 deletions pandas/tests/tseries/offsets/test_custom_business_month.py
Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
from datetime import (
date,
datetime,
timedelta,
)

import numpy as np
Expand Down Expand Up @@ -200,6 +201,59 @@ def test_datetimeindex(self):
0
] == datetime(2012, 1, 3)

@pytest.mark.parametrize(
"case",
[
(
CBMonthBegin(n=1, offset=timedelta(days=5)),
{
datetime(2021, 3, 1): datetime(2021, 4, 1) + timedelta(days=5),
datetime(2021, 4, 17): datetime(2021, 5, 3) + timedelta(days=5),
},
),
(
CBMonthBegin(n=2, offset=timedelta(days=40)),
{
datetime(2021, 3, 10): datetime(2021, 5, 3) + timedelta(days=40),
datetime(2021, 4, 30): datetime(2021, 6, 1) + timedelta(days=40),
},
),
(
CBMonthBegin(n=1, offset=timedelta(days=-5)),
{
datetime(2021, 3, 1): datetime(2021, 4, 1) - timedelta(days=5),
datetime(2021, 4, 11): datetime(2021, 5, 3) - timedelta(days=5),
},
),
(
-2 * CBMonthBegin(n=1, offset=timedelta(days=10)),
{
datetime(2021, 3, 1): datetime(2021, 1, 1) + timedelta(days=10),
datetime(2021, 4, 3): datetime(2021, 3, 1) + timedelta(days=10),
},
),
(
CBMonthBegin(n=0, offset=timedelta(days=1)),
{
datetime(2021, 3, 2): datetime(2021, 4, 1) + timedelta(days=1),
datetime(2021, 4, 1): datetime(2021, 4, 1) + timedelta(days=1),
},
),
(
CBMonthBegin(
n=1, holidays=["2021-04-01", "2021-04-02"], offset=timedelta(days=1)
),
{
datetime(2021, 3, 2): datetime(2021, 4, 5) + timedelta(days=1),
},
),
],
)
def test_apply_with_extra_offset(self, case):
offset, cases = case
for base, expected in cases.items():
assert_offset_equal(offset, base, expected)


class TestCustomBusinessMonthEnd(CustomBusinessMonthBase, Base):
_offset = CBMonthEnd
Expand Down Expand Up @@ -337,3 +391,54 @@ def test_datetimeindex(self):
assert date_range(start="20120101", end="20130101", freq=freq).tolist()[
0
] == datetime(2012, 1, 31)

@pytest.mark.parametrize(
"case",
[
(
CBMonthEnd(n=1, offset=timedelta(days=5)),
{
datetime(2021, 3, 1): datetime(2021, 3, 31) + timedelta(days=5),
datetime(2021, 4, 17): datetime(2021, 4, 30) + timedelta(days=5),
},
),
(
CBMonthEnd(n=2, offset=timedelta(days=40)),
{
datetime(2021, 3, 10): datetime(2021, 4, 30) + timedelta(days=40),
datetime(2021, 4, 30): datetime(2021, 6, 30) + timedelta(days=40),
},
),
(
CBMonthEnd(n=1, offset=timedelta(days=-5)),
{
datetime(2021, 3, 1): datetime(2021, 3, 31) - timedelta(days=5),
datetime(2021, 4, 11): datetime(2021, 4, 30) - timedelta(days=5),
},
),
(
-2 * CBMonthEnd(n=1, offset=timedelta(days=10)),
{
datetime(2021, 3, 1): datetime(2021, 1, 29) + timedelta(days=10),
datetime(2021, 4, 3): datetime(2021, 2, 26) + timedelta(days=10),
},
),
(
CBMonthEnd(n=0, offset=timedelta(days=1)),
{
datetime(2021, 3, 2): datetime(2021, 3, 31) + timedelta(days=1),
datetime(2021, 4, 1): datetime(2021, 4, 30) + timedelta(days=1),
},
),
(
CBMonthEnd(n=1, holidays=["2021-03-31"], offset=timedelta(days=1)),
{
datetime(2021, 3, 2): datetime(2021, 3, 30) + timedelta(days=1),
},
),
],
)
def test_apply_with_extra_offset(self, case):
offset, cases = case
for base, expected in cases.items():
assert_offset_equal(offset, base, expected)