Get a string from all_options

def get_string(self, key):
        """Get a string from all_options"""

        # Massive hack, lol
        if key.startswith("lambda."):
            key = "lambda.items.{0}".format(key[7:])
        if key.startswith("apigateway."):
            key = "apigateway.items.{0}".format(key[11:])

        # Make sure key is in all_options
        if key not in self.all_options:
            kwargs = {}
            if len(self.chain) > 1:
                kwargs['source'] = Meta(self.all_options, self.chain[-2]).source
            raise BadOptionFormat("Can't find key in options", key=key, chain=self.chain, **kwargs)

        return super(MergedOptionStringFormatter, self).get_string(key)