code: def to_python(self, value):
          
          assert isinstance(value, list)
  
          # convert every value in list
          value = list(value)
          for i, v in enumerate(value):
              value[i] = self.value_to_python(v)
  
          # return result
          return value
docs: Converts the input value into the expected Python data type, raising
          django.core.exceptions.ValidationError if the data can't be converted.
          Returns the converted value. Subclasses should override this.