How do I have referenced key:value update when their referenced key:value updates in a class?

In the code below, how can I change the set_ref method so that it automatically changes to value of the reference key to match the value of the key it is referencing every time I print sheet?

For Example:

In the code below, I set A1 value to 10, then I use the set_ref method to make A3 reference A1 so it’s also 10. Now when I set value of A1 to 20, A3 is still 10. What do I need to do to automatically get A3 value to change to 20?

#create sheets class with constructor to initialize "cells" instance variable as a dictionary

class Sheet:
    def __init__(self) -> None:
        self.cells = dict()

    # set_value method takes key as a string and value as an int, set cells with
    # key index along with its value
    def set_value(self, key: string, value: int) -> None:
        self.cells[key] = value

    # get_value method takes the key as a string and return the value of the cell
    # based on key index
    def get_value(self, key: string) -> int:
        return self.cells[key]
        
    # set ref takes new key, the reference key and the old key, the key being referenced
    # use set value method to set new value that has new key and the value of the key that it references
    def set_ref(self, ref_key: string, key:string):
         self.set_value(ref_key, self.cells[key])
         
    # repr dunder method returns output as a string
    # for each key in all the cells:
    # add to the output= key: and its value and return key:value pair to us
    def __repr__(self):
        output = "--------\n"
        for key in self.cells.keys():
            output += f'{key}: {self.get_value(key)}\n'
        output += "--------"
        return output


# sheet object instantiation
sheet = Sheet()

sheet.set_value('A1', 10)

sheet.set_ref('A3', 'A1') 

print(sheet) # A3 is now 10, just like A1

sheet.set_value('A1', 20)

print(sheet)  # A3 is still 10, not 20

>Solution :

Assuming that keys are always str and values are always int you can tweak your code a bit:

class Sheet:
    def __init__(self) -> None:
        self.cells = dict()

    # set_value method takes key as a string and value as an int, set cells with
    # key index along with its value
    def set_value(self, key: str, value: int) -> None:
        self.cells[key] = value

    # get_value method takes the key as a string and return the value of the cell
    # based on key index
    def get_value(self, key: str) -> int:
        if type(self.cells[key]) == int:
            return self.cells[key]
        return self.get_value(self.cells[key])
        
    # set ref takes new key, the reference key and the old key, the key being referenced
    # use set value method to set new value that has new key and the value of the key that it references
    def set_ref(self, ref_key: str, key:str):
         self.set_value(ref_key, key)
         
    # repr dunder method returns output as a string
    # for each key in all the cells:
    # add to the output= key: and its value and return key:value pair to us
    def __repr__(self):
        output = "--------\n"
        for key in self.cells.keys():
            output += f'{key}: {self.get_value(key)}\n'
        output += "--------"
        return output


# sheet object instantiation
sheet = Sheet()

sheet.set_value('A1', 10)

sheet.set_ref('A3', 'A1') 

print(sheet) # A3 is now 10, just like A1

sheet.set_value('A1', 20)

print(sheet)

output:

--------
A1: 10
A3: 10
--------
--------
A1: 20
A3: 20
--------