# 5.4 Standard Module `random`

This module implements pseudo-random number generators for various distributions: on the real line, there are functions to compute normal or Gaussian, lognormal, negative exponential, gamma, and beta distributions. For generating distribution of angles, the circular uniform and von Mises distributions are available.

The module exports the following functions, which are exactly equivalent to those in the `whrandom` module: `choice`, `randint`, `random`, `uniform`. See the documentation for the `whrandom` module for these functions.

The following functions specific to the `random` module are also defined, and all return real values. Function parameters are named after the corresponding variables in the distribution's equation, as used in common mathematical practice; most of these equations can be found in any statistics text.

`betavariate` (alpha, beta)
  Beta distribution. Conditions on the parameters are `alpha>-1` and `beta>-1`. Returned values will range between 0 and 1.

`cunifvariate` (mean, arc)
  Circular uniform distribution. mean is the mean angle, and arc is the range of the distribution, centered around the mean angle. Both values must be expressed in radians, and can range between 0 and `pi`. Returned values will range between `mean - arc/2` and `mean + arc/2`.

`expovariate` (lambd)
  Exponential distribution. lambd is 1.0 divided by the desired mean. (The parameter would be called ``lambda'', but that's also a reserved word in Python.) Returned values will range from 0 to positive infinity.

`gamma` (alpha, beta)
  Gamma distribution. (Not the gamma function!) Conditions on the parameters are `alpha>-1` and `beta>0`.

`gauss` (mu, sigma)
  Gaussian distribution. mu is the mean, and sigma is the standard deviation. This is slightly faster than the `normalvariate` function defined below.

`lognormvariate` (mu, sigma)
  Log normal distribution. If you take the natural logarithm of this distribution, you'll get a normal distribution with mean mu and standard deviation sigma mu can have any value, and sigma must be greater than zero.

`normalvariate` (mu, sigma)
  Normal distribution. mu is the mean, and sigma is the standard deviation.

`vonmisesvariate` (mu, kappa)
  mu is the mean angle, expressed in radians between 0 and pi, and kappa is the concentration parameter, which must be greater then or equal to zero. If kappa is equal to zero, this distribution reduces to a uniform random angle over the range 0 to `2*pi`.

`paretovariate` (alpha)
  Pareto distribution. alpha is the shape parameter.

`weibullvariate` (alpha, beta)
  Weibull distribution. alpha is the scale parameter, and beta is the shape parameter.

See Also:

`whrandom` (the standard Python random number generator)