BUG: Fix DateOffsets to return NotImplemented when types do not match

Enable test cases that involve these DateOffsets with `__r*` ops

Author: jtratner

pandas/tests/test_series.py

@@ -2187,23 +2187,22 @@ def test_operators_timedelta64(self):
     def test_timedeltas_with_DateOffset(self):
 
         # GH 4532
-        # commented out cases are problematic b/c of issues with Offsets
         # operate with pd.offsets
         s = Series([Timestamp('20130101 9:01'), Timestamp('20130101 9:02')])
 
         result = s + pd.offsets.Second(5)
-        # result2 = pd.offsets.Second(5) + s
+        result2 = pd.offsets.Second(5) + s
         expected = Series(
             [Timestamp('20130101 9:01:05'), Timestamp('20130101 9:02:05')])
         assert_series_equal(result, expected)
-        # assert_series_equal(result2, expected)
+        assert_series_equal(result2, expected)
 
         result = s + pd.offsets.Milli(5)
-        # result2 = pd.offsets.Milli(5) + s
+        result2 = pd.offsets.Milli(5) + s
         expected = Series(
             [Timestamp('20130101 9:01:00.005'), Timestamp('20130101 9:02:00.005')])
         assert_series_equal(result, expected)
-        # assert_series_equal(result2, expected)
+        assert_series_equal(result2, expected)
 
         result = s + pd.offsets.Minute(5) + pd.offsets.Milli(5)
         expected = Series(
@@ -2232,8 +2231,7 @@ def test_timedeltas_with_DateOffset(self):
                     'Milli', 'Nano' ]:
             op = getattr(pd.offsets,do)
             s + op(5)
-            # can't do this because DateOffset doesn't do the right thing
-            # op(5) + s
+            op(5) + s
 
         # invalid DateOffsets
         for do in [ 'Week', 'BDay', 'BQuarterEnd', 'BMonthEnd', 'BYearEnd',

pandas/tseries/offsets.py

@@ -19,6 +19,10 @@
 #----------------------------------------------------------------------
 # DateOffset
 
+class ApplyTypeError(TypeError):
+    # sentinel class for catching the apply error to return NotImplemented
+    pass
+
 
 class CacheableOffset(object):
 
@@ -128,15 +132,15 @@ def __repr__(self):
                         kwds_new[key] = self.kwds[key]
                 if len(kwds_new) > 0:
                     attrs.append('='.join((attr, repr(kwds_new))))
-            else:            
+            else:
                 if attr not in exclude:
                     attrs.append('='.join((attr, repr(getattr(self, attr)))))
 
         if abs(self.n) != 1:
             plural = 's'
         else:
             plural = ''
-        
+
         n_str = ""
         if self.n != 1:
             n_str = "%s * " % self.n
@@ -170,19 +174,21 @@ def __call__(self, other):
         return self.apply(other)
 
     def __add__(self, other):
-        return self.apply(other)
+        try:
+            return self.apply(other)
+        except ApplyTypeError:
+            return NotImplemented
 
     def __radd__(self, other):
         return self.__add__(other)
 
     def __sub__(self, other):
         if isinstance(other, datetime):
-            raise TypeError('Cannot subtract datetime from offset!')
+            raise TypeError('Cannot subtract datetime from offset.')
         elif type(other) == type(self):
             return self.__class__(self.n - other.n, **self.kwds)
         else:  # pragma: no cover
-            raise TypeError('Cannot subtract %s from %s'
-                            % (type(other), type(self)))
+            return NotImplemented
 
     def __rsub__(self, other):
         return self.__class__(-self.n, **self.kwds) + other
@@ -273,7 +279,7 @@ def __repr__(self): #TODO: Figure out if this should be merged into DateOffset
             plural = 's'
         else:
             plural = ''
-            
+
         n_str = ""
         if self.n != 1:
             n_str = "%s * " % self.n
@@ -370,8 +376,8 @@ def apply(self, other):
             return BDay(self.n, offset=self.offset + other,
                         normalize=self.normalize)
         else:
-            raise TypeError('Only know how to combine business day with '
-                            'datetime or timedelta!')
+            raise ApplyTypeError('Only know how to combine business day with '
+                                 'datetime or timedelta.')
 
     @classmethod
     def onOffset(cls, dt):
@@ -463,8 +469,8 @@ def apply(self, other):
             return BDay(self.n, offset=self.offset + other,
                         normalize=self.normalize)
         else:
-            raise TypeError('Only know how to combine trading day with '
-                            'datetime, datetime64 or timedelta!')
+            raise ApplyTypeError('Only know how to combine trading day with '
+                                 'datetime, datetime64 or timedelta.')
         dt64 = self._to_dt64(other)
 
         day64 = dt64.astype('datetime64[D]')
@@ -1177,7 +1183,10 @@ def __add__(self, other):
                 return type(self)(self.n + other.n)
             else:
                 return _delta_to_tick(self.delta + other.delta)
-        return self.apply(other)
+        try:
+            return self.apply(other)
+        except ApplyTypeError:
+            return NotImplemented
 
     def __eq__(self, other):
         if isinstance(other, compat.string_types):
@@ -1220,8 +1229,8 @@ def apply(self, other):
             return other + self.delta
         elif isinstance(other, type(self)):
             return type(self)(self.n + other.n)
-        else:  # pragma: no cover
-            raise TypeError('Unhandled type: %s' % type(other))
+        else:
+            raise ApplyTypeError('Unhandled type: %s' % type(other).__name__)
 
     _rule_base = 'undefined'