Allows set_index() to take an Index as an argument (pandas-dev#10797)

Author: michaelbilow

pandas/core/frame.py

@@ -2628,7 +2628,7 @@ def set_index(self, keys, drop=True, append=False, inplace=False,
         -------
         dataframe : DataFrame
         """
-        if not isinstance(keys, list):
+        if not com.is_list_like(keys):
             keys = [keys]
 
         if inplace: