import numpy as np
def variancediy(data1, data2=None):
    if data2 is None:
        c = data1
    else:

        data22 =[data2]

        c = data1+data22

    n = len(c)
    if n > 1:
        mean = sum(c) / n
    else:
        mean = sum(c)
    deviations = [(x - mean) ** 2 for x in c]
    if n > 1:
        variance = sum(deviations) / (n - 1)
    else:
        variance = sum(deviations)
    if len(data1) == 0:
        variance = float('inf')
    return variance