code: def force_list(data):
      
      if data is None:
          return []
      elif not isinstance(data, (list, tuple, set)):
          return [data]
      elif isinstance(data, (tuple, set)):
          return list(data)
      return data
docs: Force ``data`` to become a list.
  
      You should use this method whenever you don't want to deal with the
      fact that ``NoneType`` can't be iterated over. For example, instead
      of writing::
  
          bar = foo.get('bar')
          if bar is not None:
              for el in bar:
                  ...
  
      you can write::
  
          for el in force_list(foo.get('bar')):
              ...
  
      Args:
          data: any Python object.
  
      Returns:
          list: a list representation of ``data``.
  
      Examples:
          >>> force_list(None)
          []
          >>> force_list('foo')
          ['foo']
          >>> force_list(('foo', 'bar'))
          ['foo', 'bar']
          >>> force_list(['foo', 'bar', 'baz'])
          ['foo', 'bar', 'baz']