Using a list of variables

[Yoriz]

I think you want to call the function getSonar 3 times, sum the result and divide by 3
try

def multi_signal_cleanup():
    return sum(getSonar() for _ in range(3))/3

which is the equivalent of

def multi_signal_cleanup():
    results = []
    for _ in range(3):
        results.append(getSonar())
    return sum(results)/3