Testing if multiple objects are in a list using one "in" statement (Python)

Question

Possible Duplicate:
Python Check if all of the following items is in a list

So I want to test whether both word and word1 are in the list lst. Of course, I could write:

if word in lst and word1 in lst:
    do x

But I wondered if I could shorten that statement to something like:

if (word and word1) in lst:
    do x

Of course, that does not work, but is there anything effectively similar that will?

I tried the following, but as you can see, it does not yield the desired result.

>>> word in lst
True
>>> word1 in lst
True
>>> (word, word1) in lst
False

EDIT: Thank you for the answers, I think I have a pretty good idea of how to do this now.

Try `set(lst).issubset([word, word1])` http://stackoverflow.com/questions/3931541/python-check-if-all-of-the-following-items-is-in-a-list — Silas Ray, Sep 04 '12 at 21:19

score 10 · Accepted Answer · edited Sep 04 '12 at 21:31

10

The answers are correct (at least one of them is). However, if you're doing containment checks and don't care about order, like your example might suggest, the real answer is that you should be using sets, and checking for subsets.

words = {"the", "set", "of", "words"}
if words <= set_of_words:
   do_stuff()

edited Sep 04 '12 at 21:31

gahooa

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answered Sep 04 '12 at 21:28

Julian

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One minor flaw in this approach is that if set_of_words is shorter than words, then it will be false, is there a workaround for such an edgecase? – Kasper Thystrup Karstensen Jun 28 '23 at 10:20

score 9 · Answer 2 · answered Sep 04 '12 at 21:20

9

Make a list of your words and a generator expression checking if they are in the list:

words = ["word1", "word2", "etc"]
lst = [...]
if all((w in lst for w in words)):
    #do something

all checks if all values in an iterable are true. Because we use a generator this is still short-circuit optimized. Of course you can inline the list of words if it is not too big for a one-liner:

if all((w in lst for w in ["word1", "word2", "etc"])):
     ...

answered Sep 04 '12 at 21:20

l4mpi

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You have an extra set of parens in both examples. Genexps that are the sole arguments to callables can just be written `all(foo for foo in thing)`. – Julian Sep 04 '12 at 21:26
1

I know, but I prefer to write them explicitly inside parentheses. This makes it easier to see there's an iterable there and helps for refactoring... the extra parens come in handy using vim :) – l4mpi Sep 04 '12 at 21:31

score 2 · Answer 3 · answered Sep 04 '12 at 21:24

2

You could do it like that:

if all(current_word in lst for current_word in (word, word1)):
  do x

answered Sep 04 '12 at 21:24

tbraun89

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score 1 · Answer 4 · edited Sep 04 '12 at 22:47

Note: Do not ever use this. It is simply here to illustrate "yet another" capability of python.

A less efficient solution:

>>> from itertools import permutations
>>> lis=[0,1,2,3,4]
>>> (1,2) in (z for z in permutations(lis,2)) #loop stops as soon as permutations(lis,2) yields (1,2)
True
>>> (1,6) in (z for z in permutations(lis,2))
False
>>> (4,2) in (z for z in permutations(lis,2))
True
>>> (0,5) in (z for z in permutations(lis,2))
False
>>> (0,4,1) in (z for z in permutations(lis,3))
True
>>> (0,4,5) in (z for z in permutations(lis,3))
False

Testing if multiple objects are in a list using one "in" statement (Python)

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