Interval dtype fix

pandas/core/dtypes/dtypes.py

@@ -6,7 +6,7 @@
 import pytz
 
 from pandas._libs.interval import Interval
-from pandas._libs.tslibs import NaT, Period, Timestamp, timezones
+from pandas._libs.tslibs import NaT, Period, Timestamp, timezones, Timedelta
 
 from pandas.core.dtypes.generic import (
     ABCCategoricalIndex, ABCDateOffset, ABCIndexClass)
@@ -894,13 +894,29 @@ def __new__(cls, subtype=None):
                 if m is not None:
                     subtype = m.group('subtype')
 
-            try:
-                subtype = pandas_dtype(subtype)
-            except TypeError:
-                raise TypeError("could not construct IntervalDtype")
+        # check subtype is numeric, datetime, or timedelta
+        valid_subtype = False
+
+        # test for number
+        try:
+            if np.issubdtype(subtype, np.number):
+                valid_subtype = True
+        except TypeError:
+            pass
+        # test for datetime
+        try:
+            DatetimeTZDtype.construct_from_string(subtype)
+            valid_subtype = True
+        except TypeError:
+            pass
+        # test for timedelta
+        try:
+            Timedelta(subtype)
+            valid_subtype = True
+        except ValueError:
+            pass
 
-        if is_categorical_dtype(subtype) or is_string_dtype(subtype):
-            # GH 19016
+        if not valid_subtype:
             msg = ('category, object, and string subtypes are not supported '
                    'for IntervalDtype')
             raise TypeError(msg)
@@ -978,7 +994,7 @@ def is_dtype(cls, dtype):
                         return True
                     else:
                         return False
-                except ValueError:
+                except (ValueError, TypeError):
                     return False
             else:
                 return False

pandas/tests/dtypes/test_dtypes.py

@@ -503,7 +503,8 @@ def test_construction_generic(self, subtype):
     @pytest.mark.parametrize('subtype', [
         CategoricalDtype(list('abc'), False),
         CategoricalDtype(list('wxyz'), True),
-        object, str, '<U10', 'interval[category]', 'interval[object]'])
+        object, str, '<U10', 'interval[category]', 'interval[object]',
+        'IntervalA'])
     def test_construction_not_supported(self, subtype):
         # GH 19016
         msg = ('category, object, and string subtypes are not supported '
@@ -532,10 +533,11 @@ def test_construction_from_string_errors(self, string):
             IntervalDtype.construct_from_string(string)
 
     @pytest.mark.parametrize('string', [
-        'interval[foo]'])
+        'interval[foo]', 'IntervalA'])
     def test_construction_from_string_error_subtype(self, string):
         # this is an invalid subtype
-        msg = 'could not construct IntervalDtype'
+        msg = ('category, object, and string subtypes are not supported '
+               'for IntervalDtype')
 
         with pytest.raises(TypeError, match=msg):
             IntervalDtype.construct_from_string(string)
@@ -559,6 +561,7 @@ def test_is_dtype(self):
         assert not IntervalDtype.is_dtype('U')
         assert not IntervalDtype.is_dtype('S')
         assert not IntervalDtype.is_dtype('foo')
+        assert not IntervalDtype.is_dtype('IntervalA')
         assert not IntervalDtype.is_dtype(np.object_)
         assert not IntervalDtype.is_dtype(np.int64)
         assert not IntervalDtype.is_dtype(np.float64)