python order with prob

gistfile1.py

import random

x = ['x', 2]
y = ['y', 3]
z = ['z', 4]

SAMPLES = 100000
choices = [x,y,z]
total_weight = float(sum([k[1] for k in choices]))
vs = []
for i in range(SAMPLES):
    choices.sort(key=lambda i: random.random())
    choices.sort(key=lambda i: random.random() > i[1] / total_weight)

    vs.append([k[0] for k in choices])

print 'target distribution'
print x[1] / total_weight, y[1] / total_weight, z[1] / total_weight
print 'test distribution'
print len([k for k in vs if k[0] == 'x']) / float(SAMPLES),
print len([k for k in vs if k[0] == 'y']) / float(SAMPLES),
print len([k for k in vs if k[0] == 'z']) / float(SAMPLES)