code: def combine_columns(columns):
      
      columns_zipped = itertools.zip_longest(*columns)
      return ''.join(x for zipped in columns_zipped for x in zipped if x)
docs: Combine ``columns`` into a single string.
  
      Example:
          >>> combine_columns(['eape', 'xml'])
          'example'
  
      Args:
          columns (iterable): ordered columns to combine
  
      Returns:
          String of combined columns