Python NameError:未定义名称“Login”，函数

我是python的初学者，当我尝试创建一个函数来登录和注册时，它总是给我一个错误NameError:name'Login'没有定义，或者NameError:name'register'没有定义，如果你看到我可以改进的地方，请告诉我

print('Banking app')


start = input('Login or Register?')

# if the user wants to log in 
if start == "Login":
     Login()

def Login(self, start):
    pass
    userName = input("Enter your username: ")
    passWord = input("Enter your password: ")

    #checking for the account 
    with open('Users.txt') as f:
        if userName and passWord in f.read():
            print('UserFound')
            accountFound = True
        else:
            print("Account not found ")
            accountFound = False



if start == "Register":
    Register()

#if user wants to make a account 
def Register(self, start):
    pass
    newUser = input("Enter your desired user: ")
    newPass = input("Enter your desired password: ")

    f = open('Users.txt', 'a')
    f.write(newUser)
    f.write(newPass)
    f.close()

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您应该在调用登录函数之前定义它，注册函数也是如此

例如：

def Login():
    pass

if start == "Login":
    Login()

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另一方面，变量和函数名应该遵循小写字母和下划线样式，除非有充分的理由不这样做。