herencia1.py

class Credentials():

    def __init__(self):
        self.user = "user"
        self.password = "password"


class Service(Credentials):
    def __init__(self):
        super().__init__()
        print(self.user)

s = Service()
#[out]: "user"

herencia2.py

class Credentials():

    def __init__(self, user, password):
        self.user = user
        self.password = password


class Service(Credentials):
    def __init__(self, user, password):
        super().__init__(user, password)
        print(self.user)

s = Service()
#[out]: "user"