bugfix for FY5253 case with bunched yearends (#18550)

Author: jbrockmendel

doc/source/whatsnew/v0.22.0.txt

@@ -265,3 +265,5 @@ Other
 - Fixed a bug where creating a Series from an array that contains both tz-naive and tz-aware values will result in a Series whose dtype is tz-aware instead of object (:issue:`16406`)
 - Fixed construction of a :class:`Series` from a ``dict`` containing ``NaN`` as key (:issue:`18480`)
 - Adding a ``Period`` object to a ``datetime`` or ``Timestamp`` object will now correctly raise a ``TypeError`` (:issue:`17983`)
+- Fixed a bug where ``FY5253`` date offsets could incorrectly raise an ``AssertionError`` in arithmetic operatons (:issue:`14774`)
+-

pandas/tests/tseries/offsets/test_fiscal.py

@@ -9,6 +9,7 @@
 
 import pandas.util.testing as tm
 
+from pandas import Timestamp
 from pandas.tseries.frequencies import get_offset, _INVALID_FREQ_ERROR
 from pandas.tseries.offsets import FY5253Quarter, FY5253
 from pandas._libs.tslibs.offsets import WeekDay
@@ -604,3 +605,23 @@ def test_offset(self):
  assert_offset_equal(offset2,
  datetime(2013, 1, 15),
  datetime(2013, 3, 30))
+
+
+def test_bunched_yearends():
+ # GH#14774 cases with two fiscal year-ends in the same calendar-year
+ fy = FY5253(n=1, weekday=5, startingMonth=12, variation='nearest')
+ dt = Timestamp('2004-01-01')
+ assert fy.rollback(dt) == Timestamp('2002-12-28')
+ assert (-fy).apply(dt) == Timestamp('2002-12-28')
+ assert dt - fy == Timestamp('2002-12-28')
+
+ assert fy.rollforward(dt) == Timestamp('2004-01-03')
+ assert fy.apply(dt) == Timestamp('2004-01-03')
+ assert fy + dt == Timestamp('2004-01-03')
+ assert dt + fy == Timestamp('2004-01-03')
+
+ # Same thing, but starting from a Timestamp in the previous year.
+ dt = Timestamp('2003-12-31')
+ assert fy.rollback(dt) == Timestamp('2002-12-28')
+ assert (-fy).apply(dt) == Timestamp('2002-12-28')
+ assert dt - fy == Timestamp('2002-12-28')

pandas/tseries/offsets.py

@@ -1831,21 +1831,26 @@ def apply(self, other):
  elif n > 0:
  if other < prev_year:
  n -= 2
- # TODO: Not hit in tests
- elif other < cur_year:
+ elif prev_year < other < cur_year:
  n -= 1
- elif other < next_year:
+ elif cur_year < other < next_year:
  pass
  else:
  assert False
  else:
- if other > next_year:
+ if next_year < other:
  n += 2
- # TODO: Not hit in tests
- elif other > cur_year:
+ # TODO: Not hit in tests; UPDATE: looks impossible
+ elif cur_year < other < next_year:
  n += 1
- elif other > prev_year:
+ elif prev_year < other < cur_year:
  pass
+ elif (other.year == prev_year.year and other < prev_year and
+ prev_year - other <= timedelta(6)):
+ # GH#14774, error when next_year.year == cur_year.year
+ # e.g. prev_year == datetime(2004, 1, 3),
+ # other == datetime(2004, 1, 1)
+ n -= 1
  else:
  assert False