>>> def variance(data):
...     # Number of observations
...     n = len(data)
...     # Mean of the data
...     mean = sum(data) / n
...     # Square deviations
...     deviations = [(x - mean) ** 2 for x in data]
...     # Variance
...     variance = sum(deviations) / n
...     return variance
...

>>> variance([4, 8, 6, 5, 3, 2, 8, 9, 2, 5])
5.76