混淆，因为我无法弄清楚是什么改变了 python 中 class 的 object 的属性

Question

Here is my code `

class Cats:
    def __init__(self,name):
        self.name=name
        #print(self.name,name,"hello")
    def change_name(self,new_name):
        self.name=new_name
        return 0
        #print(new_name)

cat1=Cats("lion")
print(cat1)
print(cat1.name)


cat2=cat1.change_name("tiger")
print(cat1.name)
print(cat1)
print(cat2)

** Here is the output with my comments/opinion on the side (pls correct me if i am wrong): ** <__main__.Cats object at 0x7f84272d7640> error because I tried to print the object cat1

lion seems fine coz i printed the attribute of the object and since the name given while initialising was lion, it printed lion

tiger THIS IS WHAT I DON'T UNDERSTAND. why is this output tiger and not lion. what exactly caused this change? Bcoz when I do <<cat2=cat1.change_name("tiger"), it should just assign the value 0 to cat2 but why did it change the value in cat1?

<__main__.Cats object at 0x7f84272d7640> error bcoz i tried to print a class

0 seems fine coz chane_name function returns 0 which is assigned to cat2

I was expecting the value of cat1.name to remain the same (it should have remained lion and not changed to tiger)

Answer 1

When you call cat1.change_name("tiger") , a few things happen:

1. The name self is bound to the same object as cat1 .
2. As a result, cat1.name is changed from "lion" to "tiger"
3. change_name returns 0 , not a new instance of Cats .

After this call, cat1.name evaluates to "tiger" , not "lion" , because the value has changed.

print(cat1) outputs your "error message" because print implicitly calls str on its argument, and since Cats does not define __str__ , object.__str__ is used instead, and that produces the string you see.

print(cat2) output 0 because that's the value that was assigned to cat2 as the return value of cat1.change_name("tiger") .