为什么我的代码不返回任何内容

目前对编程和尝试学习 Python 还很陌生.我有这个代码，但我不明白为什么我没有得到返回值:(

fairly new to programming and trying to learn Python at the moment. I have this code and I don't understand why I don't get a return value :(

balance = 3200
annualInterestRate = 0.2
monthlyInterestRate = (annualInterestRate/12 + 1)


def f(x):
    m = 0
    ba = balance 
    while m < 12: 
        ba = (ba - x)*monthlyInterestRate 
        m += 1 
    return ba

def bisection():
    a = 0
    b = balance
    c = (a+b)/2
    while a != b:
        if f(c) == 0:
            return c
        elif f(c) < 0:
            a = c
        else:
            b = c

        c = (a+b)/2 

    return c



bisection()