Updated set_index example for append

Author: SaraInCode

pandas/core/frame.py

@@ -5958,16 +5958,16 @@ def set_index(
 
         Append a column to the existing index:
 
-        >>> df.set_index("month", inplace=True)
-        >>> df.set_index("year", append=True)
+        >>> a = df.set_index("month")
+        >>> a.set_index("year", append=True)
                       sale
         month  year
         1      2012    55
         4      2014    40
         7      2013    84
         10     2014    31
 
-        >>> df.set_index("year", append=False)
+        >>> a.set_index("year", append=False)
                sale
         year
         2012    55