human
I wrote the below code

    def decorator(func):
        msg = err_msg
        if (msg is None):
            msg = ('%s    is    not    re-entrant' % func.__name__)
        lock = ReentrancyLock(msg)
        return lock.decorate(func)
    return decorator

What's a good function header?
assistant
#Here's a good function header.

def non_reentrant(err_msg=None):