import functools

def log(ins):
    def decorator(func):
        @functools.wraps(func)
        def wrapper(*args, **kw):
            print('begin call')
            res = func(*args, **kw)
            print('end call')
            return res
        return wrapper

    if isinstance(ins, str):
        print(ins)
        return decorator
    else:
        return decorator(ins)

@log('execute')
def now():
    print('2015')

now()

支持有、无参数打印