Review (gfyoung)

Author: h-vetinari

doc/source/whatsnew/v0.25.0.rst

@@ -574,7 +574,7 @@ Strings
 ^^^^^^^
 
 - Bug in the ``__name__`` attribute of several methods of :class:`Series.str`, which were set incorrectly (:issue:`23551`)
-- Improved TypeError and shallower stacktrace when passing Series of wrong dtype to :meth:`Series.str.cat` (:issue:`22722`)
+- Improved error message when passing ``Series`` of wrong dtype to :meth:`Series.str.cat` (:issue:`22722`)
 -
 
 

pandas/core/strings.py

@@ -2280,11 +2280,14 @@ def cat(self, others=None, sep=None, na_rep=None, join=None):
                                  'must all be of the same length as the '
                                  'calling Series/Index.')
 
+        # data has already been checked by _validate to be of correct dtype,
+        # but others could still have Series of dtypes (e.g. integers) which
+        # will necessarily fail in concatenation. To avoid deep and confusing
+        # traces, we raise here for anything that's not object or all-NA float.
         if any(not (x.dtype == 'O' or (is_categorical_dtype(x)
                                        and x.cat.categories.dtype == 'O')
                     or (x.dtype == 'float' and x.isna().all()))
                for x in others):
-            # data has already been checked by str-accessor
             raise TypeError('Can only concatenate list-likes containing only '
                             'strings (or missing values)!')
 

pandas/tests/test_strings.py

@@ -422,6 +422,7 @@ def test_str_cat_categorical(self, box, dtype_caller, dtype_target, sep):
 
     @pytest.mark.parametrize('box', [Series, Index, np.array, list])
     def test_str_cat_raise_wrong_dtype(self, box):
+        # GH 22722
         s = Series(['a', 'b', 'c', 'd'])
         t = box([1, 2, 3, 4])