Changes according to comments

Author: kotamatsuoka

pandas/core/internals/blocks.py

@@ -1005,7 +1005,7 @@ def coerce_to_target_dtype(self, other):
         we can also safely try to coerce to the same dtype
         and will receive the same block
         """
-        if type(other) == str:
+        if isinstance(other, str):
             dtype = "string"
             if is_dtype_equal(self.dtype, dtype):
                 return self

pandas/tests/series/methods/test_replace.py

@@ -420,5 +420,6 @@ def test_replace_only_one_dictlike_arg(self):
         ],
     )
     def test_replace_dtype(self, series, to_replace, expected):
+        # GH 33484
         result = str(series.replace(to_replace).dtype)
         assert expected == result