Interval dtype fix

pandas/core/dtypes/dtypes.py

@@ -931,10 +931,15 @@ def construct_from_string(cls, string):
         attempt to construct this type from a string, raise a TypeError
         if its not possible
         """
-        if (isinstance(string, compat.string_types) and
-            (string.startswith('interval') or
-             string.startswith('Interval'))):
-            return cls(string)
+        if isinstance(string, compat.string_types):
+            if (string.lower() == 'interval' or
+               cls._match.search(string) is not None):
+                    return cls(string)
+            else:
+                msg = ('Incorrectly formatted string passed to constructor. '
+                       'Valid formats include Interval or Inverval[dtype] '
+                       'where dtype is numeric, datetime, or timedelta')
+                raise TypeError(msg)
 
         msg = "a string needs to be passed, got type {typ}"
         raise TypeError(msg.format(typ=type(string)))
@@ -978,7 +983,7 @@ 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

@@ -511,10 +511,11 @@ def test_construction_not_supported(self, subtype):
         with pytest.raises(TypeError, match=msg):
             IntervalDtype(subtype)
 
-    def test_construction_errors(self):
+    @pytest.mark.parametrize('subtype', ['xx', 'IntervalA', 'Interval[foo]'])
+    def test_construction_errors(self, subtype):
         msg = 'could not construct IntervalDtype'
         with pytest.raises(TypeError, match=msg):
-            IntervalDtype('xx')
+            IntervalDtype(subtype)
 
     def test_construction_from_string(self):
         result = IntervalDtype('interval[int64]')
@@ -523,7 +524,7 @@ def test_construction_from_string(self):
         assert is_dtype_equal(self.dtype, result)
 
     @pytest.mark.parametrize('string', [
-        'foo', 'foo[int64]', 0, 3.14, ('a', 'b'), None])
+        0, 3.14, ('a', 'b'), None])
     def test_construction_from_string_errors(self, string):
         # these are invalid entirely
         msg = 'a string needs to be passed, got type'
@@ -532,13 +533,16 @@ def test_construction_from_string_errors(self, string):
             IntervalDtype.construct_from_string(string)
 
     @pytest.mark.parametrize('string', [
-        'interval[foo]'])
+        'foo', 'foo[int64]'])
     def test_construction_from_string_error_subtype(self, string):
         # this is an invalid subtype
-        msg = 'could not construct IntervalDtype'
+        msg = ('Incorrectly formatted string passed to constructor. '
+               'Valid formats include Interval or Inverval[dtype] '
+               'where dtype is numeric, datetime, or timedelta')
 
-        with pytest.raises(TypeError, match=msg):
+        with pytest.raises(TypeError) as e:
             IntervalDtype.construct_from_string(string)
+            assert e == msg
 
     def test_subclass(self):
         a = IntervalDtype('interval[int64]')
@@ -559,6 +563,7 @@ 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)