def exists(self, key, fresh=False):
        """Check if key exists

        :param key: the name of setting variable
        :param fresh: if key should be taken from source directly
        :return: Boolean
        """
        key = upperfy(key)
        if key in self._deleted:
            return False
        return self.get(key, fresh=fresh, default=missing) is not missing
Check if key exists

        :param key: the name of setting variable
        :param fresh: if key should be taken from source directly
        :return: Boolean
        
dynaconf/base.py