Why use the __init__ constructor method in Python? [duplicate]

I would like to understand better why using __init__ by comparing these two code, I even understood that __init__ will always be started with the instantiated object, but should I always use it?

With __init__:

class Cliente():
    def __init__(self,saldo,nome):
        self.__saldo = nome
        self.__nome = saldo
    def getsaldo(self):
        return self.__saldo
    def setsaldo(self,saldo):
        self.__saldo = saldo
    def setnome(self,nome):
        self.__nome = nome
    def getnome (self):
        return self.__nome

No __init__:

class Cliente():
    __saldo = 0
    __nome = None
    def getsaldo(self):
        return self.__saldo
    def setsaldo(self,saldo):
        self.__saldo = saldo
    def setnome(self,nome):
        self.__nome = nome
    def getnome (self):
        return self.__nome