Code Wars - Common Denominators

##5 Kyu - Common Denominators

def is_common(arr, test_den):
    for j in range(len(arr)):
        if test_den % arr[j][1] != 0:   ##Check all denominators are factors of test
            return False
    return True

def convertFracts(lst):
    max_d = 0                           ##Variable to hold largest existing denominator
    for i in range(len(lst)):           ##Find the largest denominator in lst
        if lst[i][1] > max_d:
            max_d = lst[i][1]
    play = True
    counter = 2
    test = 0                             ##Just to keep test in the right scope for for loop below
    while play == True:
        test = max_d * counter           ##Creates test lowest common denominator
        if not is_common(lst, test):     ##Test not valid for all denominators
            counter += 1
        else:                            ##Test is valid, break out of loop
            play = False
    for k in lst:
        factor = test//k[1]              ##how to get to lowest common denominator
        for m in range(len(k)):          ##raises all values to match lowest common denominator
            k[m] = k[m] * factor
    return lst