Determining if a string contains a word

Question

In Python, what is the syntax for a statement that, given the following context:

words = 'blue yellow'

would be an if statement that checks to see if words contains the word "blue"? I.e.,

if words ??? 'blue':
    print 'yes'
elif words ??? 'blue':
    print 'no'

In English, "If words contain blue, then say yes. Otherwise, print no."

@DSM I was struggling to think of a word that didn't have blue as an obvious prefix or suffix ;) - nice one! — Jon Clements, Mar 13 '13 at 00:44
@DSM I think the other question already answered that but thanks — John Doe Smith, Mar 13 '13 at 00:48

score 23 · Accepted Answer · edited Mar 13 '13 at 00:53

23

words = 'blue yellow'

if 'blue' in words:
    print 'yes'
else:
    print 'no'

Edit

I just realized that nightly blues would contain blue, but not as a whole word. If this is not what you want, split the wordlist:

if 'blue' in words.split():
    …

edited Mar 13 '13 at 00:53

Mattie

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answered Mar 13 '13 at 00:39

salezica

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So basically you just flip it and put in. – John Doe Smith Mar 13 '13 at 00:41
So what the what now? – salezica Mar 13 '13 at 00:43
Lol well after your edit I read and that was not that case but ill keep that in mind. Oh and the comment I wrote made sense in my mind nvm about that lol. – John Doe Smith Mar 13 '13 at 00:44
I want it to say if it contains it at all. So I just write `if 'blue' in words`. Correct? – John Doe Smith Mar 13 '13 at 00:51

score 6 · Answer 2 · answered Mar 13 '13 at 00:44

You can use in or do explicit checks:

if 'blue ' in words:
    print 'yes'

or

if words.startswith('blue '):
    print 'yes'

Edit: Those 2 will only work if the sentence doesnt end with 'blue'. To check for that, you can do what one of the previous answers suggested

if 'blue' in words.split():
    print 'yes'

score 6 · Answer 3 · answered Mar 13 '13 at 00:51

6

You can also use regex:

\bblue\b will return True only if it can find the exact word 'blue', otherwise False.

In [24]: import re

In [25]: strs='blue yellow'

In [26]: bool(re.search(r'\bblue\b',strs))
Out[26]: True

In [27]: strs="nightly blues"

In [28]: bool(re.search(r'\bblue\b',strs))
Out[28]: False

answered Mar 13 '13 at 00:51

Ashwini Chaudhary

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mmm... Thanks but seems complicated lol. I think ill just stick to `if 'blue' in words` but great answer! – John Doe Smith Mar 13 '13 at 00:53

martega · Answer 4 · 2013-03-13T01:11:42.847

2

The easiest way to do this is probably the following:

words = set('blue yellow'.split())
if 'blue' in words:
    print 'yes'
else:
    print 'no'

If your words list is really huge, you'll get a speed increase by wrapping words.split() in set as testing set membership is more computationally efficient than testing list membership.

edited Mar 13 '13 at 01:11

answered Mar 13 '13 at 01:01

martega

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Creation of set is an `O(N)` operation in itself, so this will help only if OP wants to check for membership multiple times on the same list and the list is huge. – Ashwini Chaudhary Mar 13 '13 at 01:09

Determining if a string contains a word

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