BUG: Fix Series constructor for Categorical with index

Fixes Series constructor so that ValueError is raised when a Categorical and index of different length are given.

Author: cbertinato

doc/source/whatsnew/v0.23.0.txt

@@ -919,6 +919,7 @@ Reshaping
 - Comparisons between :class:`Series` and :class:`Index` would return a ``Series`` with an incorrect name, ignoring the ``Index``'s name attribute (:issue:`19582`)
 - Bug in :func:`qcut` where datetime and timedelta data with ``NaT`` present raised a ``ValueError`` (:issue:`19768`)
 - Bug in :func:`DataFrame.iterrows`, which would infers strings not compliant to `ISO8601 <https://en.wikipedia.org/wiki/ISO_8601>`_ to datetimes (:issue:`19671`)
+- Bug in :class:`Series` constructor with ``Categorical`` where a ```ValueError`` is not raised when an index of different length is given (:issue:`19342`)
 
 Other
 ^^^^^

pandas/core/series.py

@@ -213,11 +213,11 @@ def __init__(self, data=None, index=None, dtype=None, name=None,
 
             elif is_extension_array_dtype(data) and dtype is not None:
                 # GH12574: Allow dtype=category only, otherwise error
-                if not data.dtype.is_dtype(dtype):
-                    raise ValueError("Cannot specify a dtype '{}' with an "
-                                     "extension array of a different "
-                                     "dtype ('{}').".format(dtype,
-                                                            data.dtype))
+                if ((dtype is not None) and
+                        not is_categorical_dtype(dtype)):
+                    raise ValueError("cannot specify a dtype with a "
+                                     "Categorical unless "
+                                     "dtype='category'")
 
             elif (isinstance(data, types.GeneratorType) or
                   (compat.PY3 and isinstance(data, map))):
@@ -235,6 +235,11 @@ def __init__(self, data=None, index=None, dtype=None, name=None,
                 if not is_list_like(data):
                     data = [data]
                 index = com._default_index(len(data))
+            else:
+                if not is_scalar(data) and len(index) != len(data):
+                    raise ValueError('Length of passed values is {val}, '
+                                     'index implies {ind}'
+                                     .format(val=len(data), ind=len(index)))
 
             # create/copy the manager
             if isinstance(data, SingleBlockManager):

pandas/tests/series/test_constructors.py

@@ -400,6 +400,20 @@ def test_constructor_default_index(self):
         s = Series([0, 1, 2])
         tm.assert_index_equal(s.index, pd.Index(np.arange(3)))
 
+    @pytest.mark.parametrize('input', [[1, 2, 3],
+                                       (1, 2, 3),
+                                       list(range(3)),
+                                       pd.Categorical(['a', 'b', 'a']),
+                                       (i for i in range(3)),
+                                       map(lambda x: x, range(3))])
+    def test_constructor_index_mismatch(self, input):
+        # GH 19342
+        # test that construction of a Series with an index of different length
+        # raises an error
+        msg = 'Length of passed values is 3, index implies 4'
+        with pytest.raises(ValueError, message=msg):
+            Series(input, index=np.arange(4))
+
     def test_constructor_corner(self):
         df = tm.makeTimeDataFrame()
         objs = [df, df]