code: def flatten(nested):
      
      flat_return = list()
  
      def __inner_flat(nested,flat):
          for i in nested:
              __inner_flat(i, flat) if isinstance(i, list) else flat.append(i)
          return flat
  
      __inner_flat(nested,flat_return)
  
      return flat_return
docs: Return a flatten version of the nested argument