ins = Myclass() # ()不可省略 for i in range(2): ins.foo(i) # self.var 变

class Myclass:
    def __init__(self):
        self.var = 1
    def foo(self, var=None):
        if var is not None:
            self.var = var
        print(self.var)


ins = Myclass()  # ()不可省略
for i in range(2):
    ins.foo(i)  # self.var 变