5. 装饰器 Decorator

装饰器是 Python 的一个高级特性，其基于高阶函数，形式如下所示：

@<装饰器函数名>
def func(args,...):
	...

其等同于如下的写法：

def func(args,...):
	...
func = <装饰器函数>(func)

装饰器可以用于跟踪运行时函数的调用情况，例如我们可以使用如下的跟踪函数用作装饰器：

def tracer_1args(fn):
	def tracer(x):
		print("Calling function", fn, "on argument", x)
		return fn(x)
	return tracer

示例

@tracer_1args
def square(x):
	return x*x

@tracer_1args
def sum_of_squares(N):
	sum = 0
	for i in range(1,N+1):
		sum += square(i)
	return sum

>>> sum_of_squares(5)
Calling function <function sum_of_squares at 0x00000159B6965260> on argument 5
Calling function <function square at 0x00000159B6965120> on argument 1
Calling function <function square at 0x00000159B6965120> on argument 2
Calling function <function square at 0x00000159B6965120> on argument 3
Calling function <function square at 0x00000159B6965120> on argument 4
Calling function <function square at 0x00000159B6965120> on argument 5
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