implement is_offsetlike

pandas/core/dtypes/common.py

@@ -12,8 +12,8 @@
 from .generic import (ABCCategorical, ABCPeriodIndex,
                       ABCDatetimeIndex, ABCSeries,
                       ABCSparseArray, ABCSparseSeries, ABCCategoricalIndex,
-                      ABCIndexClass)
-from .inference import is_string_like
+                      ABCIndexClass, ABCDateOffset)
+from .inference import is_string_like, is_list_like
 from .inference import *  # noqa
 
 
@@ -266,6 +266,37 @@ def is_datetimetz(arr):
             is_datetime64tz_dtype(arr))
 
 
+def is_offsetlike(arr_or_obj):
+    """
+    Check if obj or all elements of list-like is DateOffset
+
+    Parameters
+    ----------
+    arr_or_obj : object
+
+    Returns
+    -------
+    boolean : Whether the object is a DateOffset or listlike of DatetOffsets
+
+    Examples
+    --------
+    >>> is_offsetlike(pd.DateOffset(days=1))
+    True
+    >>> is_offsetlike('offset')
+    False
+    >>> is_offsetlike([pd.offsets.Minute(4), pd.offsets.MonthEnd()])
+    True
+    >>> is_offsetlike(np.array([pd.DateOffset(months=3), pd.Timestamp.now()]))
+    False
+    """
+    if isinstance(arr_or_obj, ABCDateOffset):
+        return True
+    elif (is_list_like(arr_or_obj) and len(arr_or_obj) and
+          is_object_dtype(arr_or_obj)):
+        return all(isinstance(x, ABCDateOffset) for x in arr_or_obj)
+    return False
+
+
 def is_period(arr):
     """
     Check whether an array-like is a periodical index.

pandas/core/ops.py

@@ -30,16 +30,15 @@
     is_object_dtype, is_timedelta64_dtype,
     is_datetime64_dtype, is_datetime64tz_dtype,
     is_bool_dtype, is_datetimetz,
-    is_list_like,
+    is_list_like, is_offsetlike,
     is_scalar,
     _ensure_object)
 from pandas.core.dtypes.cast import maybe_upcast_putmask, find_common_type
 from pandas.core.dtypes.generic import (
     ABCSeries,
     ABCDataFrame,
     ABCIndex,
-    ABCPeriodIndex,
-    ABCDateOffset)
+    ABCPeriodIndex)
 
 # -----------------------------------------------------------------------------
 # Functions that add arithmetic methods to objects, given arithmetic factory
@@ -363,7 +362,7 @@ def __init__(self, left, right, name, na_op):
         rvalues = self._convert_to_array(right, name=name, other=lvalues)
 
         # left
-        self.is_offset_lhs = self._is_offset(left)
+        self.is_offset_lhs = is_offsetlike(left)
         self.is_timedelta_lhs = is_timedelta64_dtype(lvalues)
         self.is_datetime64_lhs = is_datetime64_dtype(lvalues)
         self.is_datetime64tz_lhs = is_datetime64tz_dtype(lvalues)
@@ -373,7 +372,7 @@ def __init__(self, left, right, name, na_op):
         self.is_floating_lhs = left.dtype.kind == 'f'
 
         # right
-        self.is_offset_rhs = self._is_offset(right)
+        self.is_offset_rhs = is_offsetlike(right)
         self.is_datetime64_rhs = is_datetime64_dtype(rvalues)
         self.is_datetime64tz_rhs = is_datetime64tz_dtype(rvalues)
         self.is_datetime_rhs = (self.is_datetime64_rhs or
@@ -515,7 +514,7 @@ def _convert_to_array(self, values, name=None, other=None):
                 values = np.empty(values.shape, dtype=other.dtype)
                 values[:] = iNaT
             return values
-        elif self._is_offset(values):
+        elif is_offsetlike(values):
             return values
         else:
             raise TypeError("incompatible type [{dtype}] for a "
@@ -618,15 +617,6 @@ def f(x):
 
         return lvalues, rvalues
 
-    def _is_offset(self, arr_or_obj):
-        """ check if obj or all elements of list-like is DateOffset """
-        if isinstance(arr_or_obj, ABCDateOffset):
-            return True
-        elif (is_list_like(arr_or_obj) and len(arr_or_obj) and
-              is_object_dtype(arr_or_obj)):
-            return all(isinstance(x, ABCDateOffset) for x in arr_or_obj)
-        return False
-
 
 def _align_method_SERIES(left, right, align_asobject=False):
     """ align lhs and rhs Series """

pandas/tests/dtypes/test_common.py

@@ -537,6 +537,19 @@ def test_is_complex_dtype():
     assert com.is_complex_dtype(np.array([1 + 1j, 5]))
 
 
+def test_is_offsetlike():
+    assert com.is_offsetlike(np.array([pd.DateOffset(month=3),
+                                       pd.offsets.Nano()]))
+    assert com.is_offsetlike(pd.offsets.MonthEnd())
+    assert com.is_offsetlike(pd.Index([pd.DateOffset(second=1)]))
+
+    assert not com.is_offsetlike(pd.Timedelta(1))
+    assert not com.is_offsetlike(np.array([1 + 1j, 5]))
+
+    # mixed case
+    assert not com.is_offsetlike(np.array([pd.DateOffset(), pd.Timestamp(0)]))
+
+
 @pytest.mark.parametrize('input_param,result', [
     (int, np.dtype(int)),
     ('int32', np.dtype('int32')),