docs: def eval(self, code, *args):
          """**DEPRECATED**: Evaluate a JavaScript expression in MongoDB.
  
          :Parameters:
            - `code`: string representation of JavaScript code to be
              evaluated
            - `args` (optional): additional positional arguments are
              passed to the `code` being evaluated
  
          .. warning:: the eval command is deprecated in MongoDB 3.0 and
            will be removed in a future server version.
          """
          warnings.warn("Database.eval() is deprecated",
                        DeprecationWarning, stacklevel=2)
  
          if not isinstance(code, Code):
              code = Code(code)
  
          result = self.command("$eval", code, args=args)
          return result.get("retval", None)