Question

为什么set_a不能访问MyClass实例的属性，但set_b可以？

NameError: global name 'my_instance' is not defined

代码：

#!/usr/bin/env python

class MyClass(object):
        a = 1
        b = 2

def set_a():
        my_instance.a = 5
        my_instance.b = 6

def main():
    def set_b():
            my_instance.a = 3
            my_instance.b = 4

    my_instance = MyClass()
    print my_instance.a, my_instance.b
    set_b()
    print my_instance.a, my_instance.b
    set_a()
    print my_instance.a, my_instance.b

if __name__ == "__main__":
        main()

Answer 1

将您的实例作为参数传递：

def set_a(my_a):
        my_a.a = 5
        my_a.b = 6

def main():
    def set_b(my_a):
            my_a.a = 3
            my_a.b = 4

    my_instance = MyClass()
    print my_instance.a, my_instance.b
    set_b(my_instance)
    print my_instance.a, my_instance.b
    set_a(my_instance)
    print my_instance.a, my_instance.b

if __name__ == "__main__":
        main()

Answer 2

函数set_a没有看到my_instance，因为它是在不同的范围内定义的。如果它将在main之外定义，那么它应该工作：

my_instance = None
...
def set_a(): ...
...
def main(): ...

虽然我建议将my_instance作为参数传递而不是定义为全局变量。

从函数作用域访问类实例

2 个答案: