code: def to_python(self, value):
          
          if isinstance(value, type(re.compile(''))):
              return value
          else:
              if value is None and self.null:
                  return None
              else:
                  try:
                      return self.get_compiled_regex(value)
                  except:
                      raise ValidationError('Invalid regex {0}'.format(value))
docs: Handles the following cases:
          1. If the value is already the proper type (a regex), return it.
          2. If the value is a string, compile and return the regex.
  
          Raises: A ValidationError if the regex cannot be compiled.