The inv_cdf ("Inverse Cumulative Distribution Function") method of an object of type statistics.NormalDist returns the inverse cumulative distribution function, also known as the quantile function or the percent-point function. That is, it returns the value of the random variable for which the probability that the variable is less than or equal to said value matches the value passed as an argument.

The pdf ("Probability Density Function") method of an object of type statistics.NormalDist returns the relative probability that the random variable being considered takes a value close to the value x passed as an argument.

Mathematically, this probability is the limit of P(x ≤ X < x + dx) as dx approaches zero.

The variance attribute of an object of type statistics.NormalDist returns the variance of the distribution.

The mode attribute of an object of type statistics.NormalDist returns the mode of the distribution.

The mean attribute of an object of type statistics.NormalDist returns the arithmetic mean of the distribution.