Python: sub string search

Question

I am trying to search for whole words with in a string and not sure how to do it.

str1 = 'this is'
str2 ='I think this isnt right'
str1 in str2

gives me True, but I want it to return False. How do I do this? Thank you.

I tried str2.find(str1), re.search(str1,str2), but I am not getting them to return nothing or a False.

Please help. thanks.

Daniel Roseman · Accepted Answer · 2011-10-03 16:33:50Z

3

Use the \b entity in regular expressions to match word boundaries.

re.search(r'\bthis is\b', 'I think this isnt right')

answered Oct 3, 2011 at 16:33

Daniel Roseman

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6 Comments

Zenvega Over a year ago

ok. Thanks. how do I generalize this using word1 = 'this is' and line1 = 'I think this isnt right'?

Daniel Roseman Over a year ago

Er, same way as you generalize anything else: by using variables. What are you having problems with?

Zenvega Over a year ago

I have str1 = 'this is' and str2 = 'i think this isnt right'. my syntax isnt working. re.search(str1,str2). It gives the object position. How do I make is return nothing? thanks.

Steven Rumbalski Over a year ago

@Pradeep: Notice the \b at the beginning and ending of r'\bthis is\b'. Those are word boundaries.

Zenvega Over a year ago

@StevenRumbalski, Yes, I understand. how do I pass variable instead of 'this is'? Thanks.

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jterrace · Accepted Answer · 2011-10-03 16:38:30Z

1

Another way using sets without a regular expression:

set(['this', 'is']).issubset(set('I think this isnt right'.split(' ')))

If the string is really long or you're going to keep evaluating if words are in the set, this could be more efficient. For example:

>>> words = set('I think this isnt right'.split(' '))
>>> words
set(['I', 'this', 'isnt', 'right', 'think'])
>>> 'this' in words
True
>>> 'is' in words
False

answered Oct 3, 2011 at 16:38

jterrace

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1 Comment

Steven Rumbalski Over a year ago

I believe Pradeep would want this to return false: set(['this', 'is']).issubset(set('I think this thing is wrong'.split(' '))).

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