python装饰器的实现
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方法吗
<p style="margin: 0px 0px 1.2em !important; font-size: 16px; line-height: 1.75em; padding-right: 0.5em; padding-left: 0.5em;">比如有一个add()函数被装饰,其实相当于add = decorator(add),那么decorator(add)就是这个类的实例, 执行add(a,b)的时候就是执行<strong style="color: #bf360c;">call方法了 <h1 id="-" style="margin: 20px 0px 10px; padding: 0px; font-weight: bold; color: black; font-size: 24px; border-bottom: 2px solid #aaaaaa;">参数化的装饰器 <p style="margin: 0px 0px 1.2em !important; font-size: 16px; line-height: 1.75em; padding-right: 0.5em; padding-left: 0.5em;">在装饰器中,我们在被装饰函数执行前会做一些事,在被装饰函数执行后可能也会做一些事,可是按照上面的写法,这些事情都是固定写好的,可不可以让这些动作会自定义的做些区别变化,那么参数化的装饰器能够满足这个要求
<p style="margin: 0px 0px 1.2em !important; font-size: 16px; line-height: 1.75em; padding-right: 0.5em; padding-left: 0.5em;">有了这个参数化装饰器,我们就可以在装饰函数时将参数写在括号内,也就是传入参数(这里我传的是字符串,其实没啥意义,只是为了简单表示参数) <p style="margin: 0px 0px 1.2em !important; font-size: 16px; line-height: 1.75em; padding-right: 0.5em; padding-left: 0.5em;">但是我们看到这个装饰器的实现中出现了三次def,之前的不都是出现两次吗,这次怎么出现了3次?它是怎么执行的 <p style="margin: 0px 0px 1.2em !important; font-size: 16px; line-height: 1.75em; padding-right: 0.5em; padding-left: 0.5em;">其实稍微想一下就想通了,还是按照装饰的过程来 <p style="margin: 0px 0px 1.2em !important; font-size: 16px; line-height: 1.75em; padding-right: 0.5em; padding-left: 0.5em;">之前是add = decorator(add),这次就把decorator换成decorator(‘我要做一次加法’),add = decorator(‘我要做一次加法’)(add),由于函数是一等对象,所以decorator(‘我要做一次加法’)就是装饰器中第一次返回的actual_decorator,由于闭包的特性,传递的参数绑定到了内部函数中,所以decorator执行完后,传入的’我要做一次加法’还是可以打印出来。 <p style="margin: 0px 0px 1.2em !important; font-size: 16px; line-height: 1.75em; padding-right: 0.5em; padding-left: 0.5em;">所以这个参数化的装饰器和普通的装饰器装饰的过程是一样的。 <h1 id="-" style="margin: 20px 0px 10px; padding: 0px; font-weight: bold; color: black; font-size: 24px; border-bottom: 2px solid #aaaaaa;">保存函数元数据的装饰器 <p style="margin: 0px 0px 1.2em !important; font-size: 16px; line-height: 1.75em; padding-right: 0.5em; padding-left: 0.5em;">在使用装饰器后一段时间,可能有一天我们会突然发现一点不对劲的地方,比如我们打印被装饰的函数的时候
<p style="margin: 0px 0px 1.2em !important; font-size: 16px; line-height: 1.75em; padding-right: 0.5em; padding-left: 0.5em;">我们从functools模块中引入了wraps()装饰器,用它来装饰装饰器中的inner函数,这样再次使用这个装饰器去装饰函数,它的元数据就保留下来了
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