refactor construct_from_string

Author: TomAugspurger

pandas/core/dtypes/dtypes.py

@@ -569,16 +569,16 @@ def construct_from_string(cls, string):
         >>> DatetimeTZDtype.construct_from_string('datetime64[ns, UTC]')
         datetime64[ns, UTC]
         """
-        msg = "could not construct DatetimeTZDtype"""
+        msg = "Could not construct DatetimeTZDtype from {}"
         try:
             match = cls._match.match(string)
             if match:
                 d = match.groupdict()
                 return cls(unit=d['unit'], tz=d['tz'])
-            else:
-                raise TypeError(msg)
-        except ValueError:
-            raise TypeError(msg)
+        except Exception:
+            # TODO(py3): Change this pass to `raise TypeError(msg) from e`
+            pass
+        raise TypeError(msg.format(string))
 
     def __unicode__(self):
         return "datetime64[{unit}, {tz}]".format(unit=self.unit, tz=self.tz)

pandas/tests/dtypes/test_dtypes.py

@@ -189,6 +189,10 @@ def test_construction_from_string(self):
         pytest.raises(TypeError,
                       lambda: DatetimeTZDtype.construct_from_string('foo'))
 
+    def test_construct_from_string_raises(self):
+        with pytest.raises(TypeError, match="notatz"):
+            DatetimeTZDtype.construct_from_string('datetime64[ns, notatz]')
+
     def test_is_dtype(self):
         assert not DatetimeTZDtype.is_dtype(None)
         assert DatetimeTZDtype.is_dtype(self.dtype)