Merge pull request #7195 from sinhrks/easter

BUG: Easter works incorrectly in negative offsets

Author: jreback

doc/source/v0.14.1.txt

@@ -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`)

pandas/tseries/offsets.py

@@ -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:
+            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):

pandas/tseries/tests/test_offsets.py

@@ -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))