Python Practice Lesson 12 of 22

Stats calculator: mean and variance

The mean is the plain average: add everything up, divide by how many there are - sum(nums) / len(nums). No import needed; sum and len are built-ins.

Variance measures how spread out the numbers are around that mean. The population variance - the simpler of the two variance formulas, and the one this lesson uses - is the average of the squared distance from each number to the mean: for every x in nums, compute (x - mean) ** 2, then average those. Squaring keeps distances positive (so numbers below the mean don't cancel out ones above it) and exaggerates the numbers that are furthest from it.

Your task: write mean(nums), returning the arithmetic mean of the numbers in nums. Then write variance(nums), returning the population variance - the average of (x - mean(nums)) ** 2 across every x in nums.

You'll practice:

Computing an average with sum and len
Building the variance formula from a generator expression and a call to your own mean

# Write mean(nums): the arithmetic mean (average) of the numbers in nums.
def mean(nums):
    pass

# Write variance(nums): the population variance - the average of
# (x - mean(nums)) ** 2 across every x in nums.
def variance(nums):
    pass