Reference · Statistics

stats.pvariance

stats.pvariance(list, num | null=) -> float

What it does

The population variance of a list of numbers: the mean of the squared distances from the mean, dividing by the count. It is Python's statistics.pvariance, for data that is the whole population; for a sample use stats.variance, which divides by one less. The answer is a float, computed with the compensated sums Python's fractions give.

Examples

print(stats.pvariance([1, 2, 3, 4]))print(stats.pvariance([0.0, 0.25, 0.25, 1.25, 1.5, 1.75, 2.75, 3.25]))

1.251.25

Edge cases

• One number is enough: its variance is 0.0. A constant list gives 0.0 too.
• A second argument, a mean already known, is accepted, but the answer is the spread about the data's own mean whatever is given, as in Python before 3.11: a correction in the sum cancels the difference. Leave it out, or pass null.
• Ints and floats can mix; the answer is always a float.

print(stats.pvariance([5]), stats.pvariance([7, 7, 7]))print(stats.pvariance([1, 2, 3, 4], 0), stats.pvariance([1, 2, 3, 4], 2.5), stats.pvariance([1, 2, 3, 4], null))

0.0 0.01.25 1.25 1.25

Errors

No data is a runtime error, not an error value: an empty list or null stops the request. So does an item that is not a number, or a second argument that is not a number.

print(stats.pvariance([]))

line 1: `stats.pvariance` requires at least one data point

print(stats.pvariance([1, 2], "x"))

line 1: `stats.pvariance` expects a number as argument 2, got str

Chaining

print([2, 4, 4, 4, 5, 5, 7, 9] | stats.pvariance)print([2, 4, 4, 4, 5, 5, 7, 9] | stats.pvariance | math.sqrt)

4.02.0

See also

stats.variance, stats.pstdev, stats.stdev, stats.mean

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