Using Random in Python's list comprehension

Question

I have a list of words named words and I would like to generate a list of 100 three-words elements named pwds. I want these 3 words to be randomly picked from the words list for each element of the pwds list, and I'd like to use list comprehension to do this.

This solution works :

pwds = [random.choice(words)+' '+random.choice(words)+' '+random.choice(words) for i in range(0,100)]

It generates a list that looks like : ['correct horse battery', 'staple peach peach', ...]

But I was looking for a way that prevents repetiting 3 times random.choice(words), so I tried this :

pwds = [(3*(random.choice(words)+' ')).strip() for i in range(0,100)]

But unfortunately, this solution makes each element having the same word three times (for example : ['horse horse horse', 'staple staple staple', ...]), which is expected to happend.

Do you know a way to pick 3 random words without repetition (EDIT : by "repetition", I mean the code repetition, not the random words repetition) ?

EDIT : My question is different than the one it has been marked as duplicate of because I'm looking for using list comprehension here. I know how I could generate different numbers, I'm just looking for specific way to do it.

@jonrsharpe: This function is great, I came up with this solution : pwds = [' '.join(random.sample(words,3)) for i in range(0,100)]. But this function prevents the possibility that the same word occurs 2 or 3 times in the same element. — Seeven
– Seeven, Commented Aug 29, 2014 at 9:30

jonrsharpe · Accepted Answer · 2014-08-29 09:40:38Z

2

If you want the words to be able to repeat within each triplet, I think what you want is something like:

pwds = [" ".join(random.choice(words) for _ in range(3)) for _ in range(100)]

Note the use of _ to indicate that we don't actually use the numbers generated by either range, and the fact that range(0, n) is the same as range(n).

A somewhat shorter example:

>>> import random
>>> words = ['correct', 'horse', 'battery', 'staple']
>>> [" ".join(random.choice(words) for _ in range(3)) for _ in range(5)]
['horse horse correct', 
 'correct staple staple', 
 'correct horse horse', 
 'battery staple battery', 
 'horse battery battery']

answered Aug 29, 2014 at 9:40

jonrsharpe

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1 Comment

Seeven Over a year ago

Thanks, it's exactly what I was looking for! Thanks for your coding advice too.

Gabz · Accepted Answer · 2014-08-29 09:52:22Z

1

You can use the join function and a list comprehension to not repeat random.choice

pwds = [' '.join([random.choice(words) for _ in range(3)]) for _ in range(100)]

answered Aug 29, 2014 at 9:52

Gabz

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4 Comments

Seeven Over a year ago

Although it is the same answer than jonrsharpe, yours helps to understand that we are using a nested list comprehension, which I didn't understand at first.

Gabz Over a year ago

Absolutly, jonrsharpe was just faster than me.

jonrsharpe Over a year ago

Actually, this is slightly better than my approach, as passing a list (rather than the bare generator expression) to str.join is more efficient - see stackoverflow.com/a/9061024/3001761

jonrsharpe Over a year ago

@SeevenByakko no problem. It won't make much difference with three items, but it's worth knowing about.

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