Before call strategy that logs to some logger the attempt.

def before_sleep_log(logger, log_level):
    """Before call strategy that logs to some logger the attempt."""
    def log_it(retry_state):
        if retry_state.outcome.failed:
            verb, value = 'raised', retry_state.outcome.exception()
        else:
            verb, value = 'returned', retry_state.outcome.result()

        logger.log(log_level,
                   "Retrying %s in %s seconds as it %s %s.",
                   _utils.get_callback_name(retry_state.fn),
                   getattr(retry_state.next_action, 'sleep'),
                   verb, value)
    return log_it