all possible combinations

John Machin sjmachin at lexicon.net
Thu Jul 14 01:02:51 CEST 2005


rbt wrote:
> On Wed, 2005-07-13 at 10:21 -0400, rbt wrote:
> 
>>Say I have a list that has 3 letters in it:
>>
>>['a', 'b', 'c']
>>
>>I want to print all the possible 4 digit combinations of those 3
>>letters:
>>
>>4^3 = 64
>>
>>aaaa
>>abaa
>>aaba
>>aaab
>>acaa
>>aaca
>>aaac
>>...
>>
>>What is the most efficient way to do this? 
> 
> 
> Expanding this to 4^4 (256) to test the random.sample function produces
> interesting results. It never finds more than 24 combinations out of the

Uh-oh -- there's that word again! What you mean to say is that it never 
finds more than 24 *PERMUTATIONS*.

1. google("define: permutation")
2. Consider that 24 == 4 * 3 * 2 * 1
3. RTFM("random.sample"), paying particular attention to the word "unique"

> possible 256. This leads to the question... how 'random' is sample ;)
> 
> Try it for yourselves:
> 
> test = list('1234')
> 
> combinations = []
> while 1:
>     combo = random.sample(test, 4)
>     possibility = ''.join(combo)
>     if possibility not in combinations:
>         print possibility    
>         combinations.append(possibility)
>         continue
>     else:
>         continue
> 

Instead of the utterly pointless continue/else/continue, shouldn't you 
have some method (other than keyboard interrupt) of jumping off the 
merry-go-round?



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