ENH: DataFrame.explode() multiple columns

Now explode() can also take in a list of columns and explode them all, given that for every record in the dataframe the elements of the exploding columns all have the same length

pandas/core/frame.py

@@ -6298,7 +6298,7 @@ def explode(self, columns: Union[str, List[str]]) -> "DataFrame":
         lengths_equal = []
 
         for row in self[columns].iterrows():
-            # converts non-lists into 1 element lists
+            # converts non-lists into 1 element lists so len() is valid
             r=row[1].apply(lambda x: x if type(x) in (list,tuple) else [x]) 
 
             # make sure all lists in the same record are the same length