python 的__call__函数

python 有一组内置（built-in）方法，__call__就是其中一种。__call__方法使python类的实例化对象可以像函数一样被调用。

具体而言，当一个类定义了__call__方法，则它的实例化对象作为函数调用时：x(arg1, arg2, ...)等价于x.__call__(arg1, arg2, ...).

例子一

class Example:
    def __init__(self):
        print("Instance Created")
      
    # 定义__call__方法
    def __call__(self):
        print("Instance is called via special method")

# 实例化一个 Example 类的对象 e
e = Example()
# 输出：Instance Created
# __call__方法将被对象 e 调用
e()
# 输出：Instance is called via special method

例子二

class Product:
    def __init__(self):
        print("Instance Created")
  
    # Defining __call__ method
    def __call__(self, a, b):
        print(a * b)

# Instance created
ans = Product()
# output: Instance Created
# __call__ method will be called
ans(10, 20)
# output: 200