code: def force_list(value, min=None, max=None):
      
      if not isinstance(value, (list, tuple)):
          value = [value]
      return is_list(value, min, max)
docs: Check that a value is a list, coercing strings into
      a list with one member. Useful where users forget the
      trailing comma that turns a single value into a list.
  
      You can optionally specify the minimum and maximum number of members.
      A minumum of greater than one will fail if the user only supplies a
      string.
  
      >>> vtor = Validator()
      >>> vtor.check('force_list', ())
      []
      >>> vtor.check('force_list', [])
      []
      >>> vtor.check('force_list', 'hello')
      ['hello']