code: def run(self, value):
          
          if self.pass_ and not value.strip():
              return True
  
          if (value.strip() if self.strip else value) not in self.given_list:
              self.error = self.error.format(value)
              return False
          return True
docs: Checks if value is included within self.given_list.
          Keyword arguments:
          value str -- the value of the associated field to compare