Review (jreback)

doc/source/whatsnew/v0.24.0.rst

@@ -374,8 +374,8 @@ Backwards incompatible API changes
 
 - A newly constructed empty :class:`DataFrame` with integer as the ``dtype`` will now only be cast to ``float64`` if ``index`` is specified (:issue:`22858`)
 - :meth:`Series.str.cat` will now raise if `others` is a `set` (:issue:`23009`)
-- The `.str`-accessor will perform more rigorous type checking for inputs. Previously, some types that were never intended to be used
-  "worked" purely due to limitations of dtype checking -- e.g. ``bytes``, which is now disabled except for `decode` and `len` (:issue:`23011`, :issue:`23163`)
+- The `.str`-accessor will perform more rigorous type checking for inputs. Previously, some types that were never intended to be used,
+  "worked" due to limitations of dtype checking -- e.g. ``bytes``, which is now disabled except for `decode` and `len` (:issue:`23011`, :issue:`23163`)
 - Passing scalar values to :class:`DatetimeIndex` or :class:`TimedeltaIndex` will now raise ``TypeError`` instead of ``ValueError`` (:issue:`23539`)
 - ``max_rows`` and ``max_cols`` parameters removed from :class:`HTMLFormatter` since truncation is handled by :class:`DataFrameFormatter` (:issue:`23818`)
 - :meth:`read_csv` will now raise a ``ValueError`` if a column with missing values is declared as having dtype ``bool`` (:issue:`20591`)

pandas/core/strings.py

@@ -1777,8 +1777,6 @@ def forbid_nonstring_types(forbidden, name=None):
 
     # deal with None
     forbidden = [] if forbidden is None else forbidden
-    # deal with single string instead of list
-    forbidden = [forbidden] if isinstance(forbidden, str) else forbidden
 
     allowed_types = {'string', 'unicode', 'empty',
                      'bytes', 'mixed', 'mixed-integer'} - set(forbidden)