def METHOD_NAME(self, size, sizer):
    # return scaled size based on sizer, where sizer (n, None) scales x
    # to n and (None, n) scales y to n
    size_new = list(sizer)
    i = size_new.index(None)
    j = i * -1 + 1
    size_new[i] = (size_new[j] * size[i]) / size[j]
    return tuple(size_new)