如何在post函数之外使用变量？

var_name = "Hello"

def post():
    global var_name
    var_name = "World"

post()
print(var_name)  # 输出：World

def post():
    var_name = "World"
    return var_name

result = post()
print(result)  # 输出：World

class MyClass:
    var_name = "Hello"

    def post(self):
        self.var_name = "World"

obj = MyClass()
obj.post()
print(obj.var_name)  # 输出：World

def outer():
    var_name = "Hello"

    def inner():
        nonlocal var_name
        var_name = "World"

    inner()
    return var_name

result = outer()
print(result)  # 输出：World