code: def eval(self, keys):
          
          for k, v in keys.items():  # pylint: disable=invalid-name
              if k in self.app.config:
                  try:
                      val = ast.literal_eval(self.app.config[k])
                      if isinstance(val, v):
                          if self.verbose_mode:
                              print(
                                  " * Casting a specified var as literal:"
                                  " {0} => {1}".format(k, v)
                              )
                          self.app.config[k] = val
                      else:
                          print(
                              " ! Does not match with specified type:"
                              " {0} => {1}".format(k, v))
                  except (ValueError, SyntaxError):
                      print(" ! Could not evaluate as literal type:"
                            " {0} => {1}".format(k, v))
docs: Examples:
              Specify type literal for key.
  
              >>> env.eval({MAIL_PORT: int})