How to handle exceptions in a nested method chain and revert changes in intermediate method?

def method1(self):
    try:
        self.method2()
    except CustomException:
        print("Error")
def method2(self):
    self.a = 3
    self.method3()

def method3(self):
    raise CustomException

How can I cancel the assignment self.a = 3 in the intermediate method (method2), when the exception in method3 occurs, such that I obtain the cleanest code?

>Solution :

Handle the exception in method 2 to reset the variable and rethrow the error, so you can catch it in method 1:

def method1(self):
    try:
        self.method2()
    except CustomException:
        print("Error")

def method2(self):
    self.a = 3

    try:
        self.method3()
    except CustomException as e:
        self.a = None  # Reset self.a
        raise e

def method3(self):
    raise CustomException