I have a regex that matches all three characters words in a string:
\b[^\s]{3}\b
When I use it with the string:
And the tiger attacked you.
this is the result:
regex = re.compile("\b[^\s]{3}\b")
regex.findall(string)
[u'And', u'the', u'you']
As you can see it matches you as a word of three characters, but I want the expression to take "you." with the "." as a 4 chars word.
I have the same problem with ",", ";", ":", etc.
I'm pretty new with regex but I guess it happens because those characters are treated like word boundaries.
Is there a way of doing this?
Thanks in advance,
Thaks to the answers of @BrenBarn and @Kendall Frey I managed to get to the regex I was looking for:
(?<!\w)[^\s]{3}(?=$|\s)
If you want to make sure the word is preceded and followed by a space (and not a period like is happening in your case), then use lookaround .
(?<=\s)\w{3}(?=\s)
If you need it to match punctuation as part of words (such as 'in.') then \\w
won't be adequate, and you can use \\S
(anything but a space)
(?<=\s)\S{3}(?=\s)
As described in the documentation :
A word is defined as a sequence of alphanumeric or underscore characters, so the end of a word is indicated by whitespace or a non-alphanumeric, non-underscore character.
So if you want a period to count as a word character and not a word boundary, you can't use \\b
to indicate a word boundary. You'll have to use your own character class. For instance, you can use a regex like \\s[^\\s]{3}\\s
if you want to match 3 non-space characters surrounded by spaces. If you still want the boundary to be zero-width (ie, restrict the match but not be included in it), you could use lookaround, something like (?<=\\s)[^\\s]{3}(?=\\s)
.
This would be my approach. Also matches words that come right after punctuations.
import re
r = r'''
\b # word boundary
( # capturing parentheses
[^\s]{3} # anything but whitespace 3 times
\b # word boundary
(?=[^\.,;:]|$) # dont allow . or , or ; or : after word boundary but allow end of string
| # OR
[^\s]{2} # anything but whitespace 2 times
[\.,;:] # a . or , or ; or :
)
'''
s = 'And the tiger attacked you. on,bla tw; th: fo.tes'
print re.findall(r, s, re.X)
output:
['And', 'the', 'on,', 'bla', 'tw;', 'th:', 'fo.', 'tes']
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