如何在python中做条件装饰器 [英] how to do a conditional decorator in python

问题描述

是否可以有条件地修饰一个函数。例如，我想用计时器函数（ timeit ）装饰函数 foo（），只有do_performance_analysis是 True （请参见下面的伪代码）。

Is it possible to decorator a function conditionally. For example, I want to decorate the function foo() with a timer function (timeit) only doing_performance_analysis is True (see the psuedo-code below).

if doing_performance_analysis:
  @timeit
  def foo():
    """
    do something, timeit function will return the time it takes
    """
    time.sleep(2)
else:
  def foo():
    time.sleep(2)  

推荐答案

装饰器是简单的可调用函数，它们返回替换项，可以选择是相同的函数，包装器或完全不同的东西。这样，您可以创建一个条件装饰器：

Decorators are simply callables that return a replacement, optionally the same function, a wrapper, or something completely different. As such, you could create a conditional decorator:

def conditional_decorator(dec, condition):
    def decorator(func):
        if not condition:
            # Return the function unchanged, not decorated.
            return func
        return dec(func)
    return decorator

现在您可以像这样使用它了：

Now you can use it like this:

@conditional_decorator(timeit, doing_performance_analysis)
def foo():
    time.sleep(2)  

装饰器也可以是一个类：

The decorator could also be a class:

class conditional_decorator(object):
    def __init__(self, dec, condition):
        self.decorator = dec
        self.condition = condition

    def __call__(self, func):
        if not self.condition:
            # Return the function unchanged, not decorated.
            return func
        return self.decorator(func)

这里的 __ call __ 方法与第一个示例中返回的 decorator（）嵌套函数以及封闭的<$此处的c $ c> dec 和 condition 参数作为参数存储在实例上，直到应用装饰器为止。

Here the __call__ method plays the same role as the returned decorator() nested function in the first example, and the closed-over dec and condition parameters here are stored as arguments on the instance until the decorator is applied.

这篇关于如何在python中做条件装饰器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！