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CHAPTER 10 ■ BATTERIES INCLUDED 229
random number in the range from 1 to 10 (inclusive), you would use randrange(1,11) (or, alternatively,
randrange(10)+1), and if you want a random odd positive integer lower than 20, you
would use randrange(1,20,2).
The function random.choice chooses (uniformly) a random element from a given sequence.
The function random.shuffle shuffles the elements of a (mutable) sequence randomly,
such that every possible ordering is equally likely.
The function random.sample chooses (uniformly) a given number of elements from a given
sequence, making sure that they’re all different.
■Note For the statistically inclined, there are other functions similar to uniform that return random numbers
sampled according to various other distributions, such as betavariate, exponential, Gaussian, and several others.
Examples
Generating a random date in a given range. In the following examples, I use several of the functions from the
time module described previously. First, let’s get the real numbers representing the limits of the time interval (the
year 2005). You do that by expressing the date as a time tuple (using -1 for day of the week, day of the year, and
daylight savings, making Python calculate that for itself) and calling mktime on these tuples:
from random import *
from time import *
date1 = (2005, 1, 1, 0, 0, 0, -1, -1, -1)
time1 = mktime(date1)
date2 = (2006, 1, 1, 0, 0, 0, -1, -1, -1)
time2 = mktime(date2)
Then you generate a random number uniformly in this range (the upper limit excluded):
>>> random_time = uniform(time1, time2)
Then, you simply convert this number back to a legible date:
>>> print asctime(localtime(random_time))
Mon Jun 24 21:35:19 2005
Creating an electronic die-throwing machine. For this example, let’s ask the user how many dice to throw, and
how many sides each one should have. The die-throwing mechanism is implemented with randrange and a for
loop:
from random import randrange
num = input('How many dice? ')
sides = input('How many sides per die? ')
sum = 0
for i in range(num): sum += randrange(sides) + 1
print 'The result is', sum