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BUG: Easter works incorrectly in negative offsets #7195

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Merged
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Jun 3, 2014
Merged

BUG: Easter works incorrectly in negative offsets #7195

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1 change: 1 addition & 0 deletions doc/source/v0.14.1.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -86,3 +86,4 @@ Bug Fixes
wouldn't test ``True`` when it encountered an ``inf``/``-inf``
(:issue:`7315`).
- Bug in inferred_freq results in None for eastern hemisphere timezones (:issue:`7310`)
- Bug in ``Easter`` returns incorrect date when offset is negative (:issue:`7195`)
14 changes: 9 additions & 5 deletions pandas/tseries/offsets.py
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Expand Up @@ -1846,12 +1846,16 @@ def apply(self, other):
currentEaster = datetime(currentEaster.year, currentEaster.month, currentEaster.day)

# NOTE: easter returns a datetime.date so we have to convert to type of other
if other >= currentEaster:
new = easter(other.year + self.n)
elif other < currentEaster:
new = easter(other.year + self.n - 1)
if self.n >= 0:
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@sinhrks This checks self.n >= 0 while pretty much all other offsets check self.n > 0. Is this difference intentional? If so I'd like to add a brief comment explaining why.

Up-to-date location for this check:
https://github.com/pandas-dev/pandas/blob/master/pandas/tseries/offsets.py#L2129

Examples for other offset classes:
https://github.com/pandas-dev/pandas/blob/master/pandas/tseries/offsets.py#L950
https://github.com/pandas-dev/pandas/blob/master/pandas/tseries/offsets.py#L1409
https://github.com/pandas-dev/pandas/blob/master/pandas/tseries/offsets.py#L1572
https://github.com/pandas-dev/pandas/blob/master/pandas/tseries/offsets.py#L1053

if other >= currentEaster:
new = easter(other.year + self.n)
else:
new = easter(other.year + self.n - 1)
else:
new = other
if other > currentEaster:
new = easter(other.year + self.n + 1)
else:
new = easter(other.year + self.n)

# FIXME: There has to be a better way to do this, but I don't know what it is
if isinstance(other, Timestamp):
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14 changes: 14 additions & 0 deletions pandas/tseries/tests/test_offsets.py
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Expand Up @@ -2483,16 +2483,30 @@ def test_onOffset(self):
def assertEq(offset, base, expected):
actual = offset + base
actual_swapped = base + offset
actual_apply = offset.apply(base)
try:
assert actual == expected
assert actual_swapped == expected
assert actual_apply == expected
except AssertionError:
raise AssertionError("\nExpected: %s\nActual: %s\nFor Offset: %s)"
"\nAt Date: %s" %
(expected, actual, offset, base))

def test_Easter():
assertEq(Easter(), datetime(2010, 1, 1), datetime(2010, 4, 4))
assertEq(Easter(), datetime(2010, 4, 5), datetime(2011, 4, 24))
assertEq(Easter(2), datetime(2010, 1, 1), datetime(2011, 4, 24))

assertEq(Easter(), datetime(2010, 4, 4), datetime(2011, 4, 24))
assertEq(Easter(2), datetime(2010, 4, 4), datetime(2012, 4, 8))

assertEq(-Easter(), datetime(2011, 1, 1), datetime(2010, 4, 4))
assertEq(-Easter(), datetime(2010, 4, 5), datetime(2010, 4, 4))
assertEq(-Easter(2), datetime(2011, 1, 1), datetime(2009, 4, 12))

assertEq(-Easter(), datetime(2010, 4, 4), datetime(2009, 4, 12))
assertEq(-Easter(2), datetime(2010, 4, 4), datetime(2008, 3, 23))

def test_Hour():
assertEq(Hour(), datetime(2010, 1, 1), datetime(2010, 1, 1, 1))
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