random import works?

[msword]

BPO	1621367
Files	random checker.py: Checks if random.choice() is all that random

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GitHub fields:

assignee = None
closed_at = <Date 2006-12-26.08:54:26.000>
created_at = <Date 2006-12-23.17:04:36.000>
labels = ['extension-modules', 'invalid']
title = 'random import works?'
updated_at = <Date 2006-12-26.08:54:26.000>
user = 'https://bugs.python.org/msword'

bugs.python.org fields:

activity = <Date 2006-12-26.08:54:26.000>
actor = 'mark-roberts'
assignee = 'none'
closed = True
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2006-12-23.17:04:36.000>
creator = 'msword'
dependencies = []
files = ['2258']
hgrepos = []
issue_num = 1621367
keywords = []
message_count = 4.0
messages = ['30861', '30862', '30863', '30864']
nosy_count = 3.0
nosy_names = ['mark-roberts', 'msword', 'dallison']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1621367'
versions = ['Python 2.5']

[msword]

I'm just starting working with python, and it seems that random.choice() isn't all that random. After running the program(attached) a few times, each and every time it selects 1 < 2 < 3 < 4 < 5 and I can expect this to happen, meaning it isn't all that random.
Email: Kentsfx2@gmail.com

Thanks

[dallison]

I believe the problem is with your test framework and not with random.choice(). The library function random.choice( seq ) selects, using a uniform distribution, one item from the sequence at each call. By the law of large numbers, if you have K items in the sequence, each should be returned K/N times, on average, after N calls. You should expect deviations even for fairly large N. If you want to test the randomess, use a chi-square test to test against the hypothes of uniform random selection with replacement. Of course there are many other statistical properties which ought to be checked, for example, the distribution of runs.

Consider the program:

import random
dist = [0,0,0,0,0]
for i in range(100000):
	j = random.choice([0,1,2,3,4])
	dist[j] += 1
print dist

which prints the distribution observed for each choice. With
100000 tries you'd expect each one to appear (on average) 20000
time. Running it on my a three times gives:

[19839, 19871, 19996, 20035, 20259]
[20043, 19870, 20025, 20109, 19953]
[19947, 20033, 19970, 20111, 19939]

[mark-roberts]

This is an issue with the way you have written your initial application. See the attachment that I've supplied to explain what is going wrong in your program. It really boils down to you adding X to each value, while X is steadily increasing in value (1, 2, 3, 4, 5). At one point, you actually add 1 to one value, and add 5 to another (for the same random choice).

• Mark

[mark-roberts]

Sorry, it appears that I can't upload a file, or I'm missing the button. Anyway, you can find the file you're lookign for here:

http://www.pandapocket.com/python/rand2.pys