Why my python code will continue run the code in the "else" after return true [duplicate]

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• Why does my recursive python function return None? 4 answers

The res will change like this 19,82,68,100,1. But when res == 1,the code will still run to isHappy(res). I don't know why it run like this.

I have debugged the code, but I don't know why it will still run to else even it meets res == 1;

def isHappy(n):

    res = 0
    for i in range(len(str(n))):
        num = int(str(n)[i])
        res += pow(num, 2)

    if res == 1:
        return True
    else:
        isHappy(res)

print(isHappy(19))

Excepted: True Actually: None