Beginning Python - From Novice to Professional

228 CHAPTER 10 ■ BATTERIES INCLUDED
random
The random module contains functions that return random numbers, which can be useful for
simulations or any program that generates random output.
■Note Actually, the numbers generated are pseudo-random. That means that while they appear completely
random, there is a predictable system that underlies them. However, because the module is so good at
pretending to be random, you probably won’t ever have to worry about this (unless you want to use these
numbers for strong-cryptography purposes, in which case they may not be “strong” enough to withstand
determined attack—but if you’re into strong cryptography, you surely don’t need me to explain such elementary
issues). If you need real randomness, you should check out the urandom function of the os module. The class
SystemRandom in the random module is based on the same kind of functionality, and gives you data that is
close to real randomness.
Some important functions in this module are shown in Table 10-7.
Table 10-7. Some Important Functions in the random Module
Function
Description
random() Returns a random real number n such that 0 ≤ n < 1
getrandbits(n)
uniform(a, b)
randrange([start], stop, [step])
choice(seq)
shuffle(seq[, random])
sample(seq, n)
Returns n random bits, in the form of a long integer
Returns a random real number n such that a ≤ n < b
Returns a random number from range(start, stop,
step)
Returns a random element from the sequence seq
Shuffles the sequence seq in place
Chooses n random, unique elements from the
sequence seq
The function random.random is one of the most basic random functions; it simply returns
a pseudo-random number n such that 0 < n < 1. Unless this is exactly what you need, you
should probably use one of the other functions, which offer extra functionality. The function
random.getrandbits returns a given number of bits (binary digits), in the form of a long integer.
This is probably mostly useful if you’re really into random stuff (for example, working with
cryptography).
The function random.uniform, when supplied with two numerical parameters a and b,
returns a random (uniformly distributed) real number n such that a < n < b. So, for example,
if you want a random angle, you could use uniform(0,360).
The function random.randrange is the standard function for generating a random integer
in the range you would get by calling range with the same arguments. For example, to get a