How can I search for a word in a file which is preceded and followed by a space in Python?

Question

I want to search a file line by line for a particular word but I want to make sure that this particular word is being preceded and followed by a space.

I know that I have to do this using regex. I've been reading this guide but it's confusing to me how to apply both lookahead and lookbehind in the same statement.

How can I do this?

counter = 0
out = open('out.txt', 'w')
with open(original_db, 'r') as db:
    for line in db:
        if re.search(word, line, re.IGNORECASE):
            counter += 1
            out.write(line)
print("Entries found for word: " + str(counter))

Why not `split` the line and check if the word is present in the resulting list? — Wiktor Stribiżew, Nov 21 '16 at 09:15
Please include more details, otherwise, it is not clear. Does it mean you also want to only match the "word" if it is not at the start/end of the line? — Wiktor Stribiżew, Nov 21 '16 at 09:26

score 5 · Accepted Answer · answered Nov 21 '16 at 09:27

5

You could add word boundary anchors, \b, to your pattern:

if re.search('\b{}\b'.format(re.escape(word)), line, re.IGNORECASE):

These only match when a word character (a-z, 0-9 or _ characters) is preceded or followed by another, non-word character. This is broader than whitespace; words preceded or followed by punctuation also work.

If you must only match words that are whitespace-separated, then don't use a regular expression; just split on whitespace:

if word in line.lower().split():

answered Nov 21 '16 at 09:27

Martijn Pieters

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Too fast for me as usual, nice answer :) – Trev Davies Nov 21 '16 at 09:32
`if re.search('\b{}\b'.format(re.escape(word)), line, re.IGNORECASE):` returned zero results but the splitter worked fine. Thank you for the quick response. – Aventinus Nov 21 '16 at 09:37
Hopefully you filled the variable 'word' with your word? – Trev Davies Nov 21 '16 at 09:39
@Aventinus without seeing a sample word that's hard to debug. Glad splitting works. – Martijn Pieters Nov 21 '16 at 09:46

How can I search for a word in a file which is preceded and followed by a space in Python?

1 Answers1