Achieving singleton pattern in python using only __init__ and not using __new__

I am trying to achieve singleton in python. Why is the below code wrong in achieving singleton pattern in Python?

class test:
    _instance = []

    def __init__(self):
        if len(test._instance)!=0:
            print('Object instantiated')
            self = test._instance[0]
        else:
            test._instance.append(self)

a = test()
print(a)
b = test()
print(b)

The output:

<__main__.test object at 0x0000023094388400>
Object instantiated
<__main__.test object at 0x00000230949D6700>

Expected Object 'b' to be same as 'a'