python capture from regex

Question

I am writing a regex to find a ? and capture everything before that. Here's what I have so far.

f = 'file.doc?gs_f'
f1 = re.search(r'(\?)',f)
print(f[:f1.start()]) #prints "file.doc"

How do I use the regex to capture everything before the ?. The is something called a look behind but I am unsure how to use it.

Possible duplicate of [Extract string with Python re.match](https://stackoverflow.com/questions/13423624/extract-string-with-python-re-match) — Corion, Jan 04 '19 at 19:39
Possible duplicate of [How would I get everything before a : in a string Python](https://stackoverflow.com/questions/27387415/how-would-i-get-everything-before-a-in-a-string-python) — Dani Mesejo, Jan 04 '19 at 19:40
... also https://stackoverflow.com/questions/11171045/python-regular-expression-example — Corion, Jan 04 '19 at 19:43

Amit Amola · Accepted Answer · 2019-01-04T19:54:45.740

1

This would work:

^[^\?]+

And use findall:

f = 'file.doc?gs_f'
f1 = re.findall("^[^\?]+",f)

You can see a regex working below for any kind of string: Regex_Working

edited Jan 04 '19 at 19:54

answered Jan 04 '19 at 19:43

Amit Amola

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I wanted to get better with regexpressions. – user3525290 Jan 04 '19 at 19:46
Oh, I see, okay, give me a minute, I'll make edits and get back with regex answer. – Amit Amola Jan 04 '19 at 19:47
Thanks. I know it has something to do with using `<=` but I tried placing that but I kept getting `none` when I print `f1.group(0)` or `f1.group(1)` – user3525290 Jan 04 '19 at 19:48
Get rid of the backslash in square brackets. – Jan Jan 04 '19 at 20:17

score 1 · Answer 2 · answered Jan 04 '19 at 19:51

1

Multiple possibilities:

Either everything not a question mark: [^?]+
Or a lazy quantifier with capturing groups: (.+?)\?
Or a positive lookahead: .+?(?=\?)

See the corresponding demos on regex101.com (1, 2 and 3).

answered Jan 04 '19 at 19:51

Jan

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Thanks everyone for all of the help – user3525290 Jan 04 '19 at 20:02

score 1 · Answer 3 · answered Jan 04 '19 at 19:55

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You do not need look behind.

f = 'file.doc?gs_f'
re.search(r'([\w\.]*(?=\?))',f).group(0)

A good here Regex lookahead, lookbehind and atomic groups

answered Jan 04 '19 at 19:55

mad_

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score 1 · Answer 4 · answered Jan 04 '19 at 19:57

Yes, it is called Positive Look Ahead. You have to look ahead till ? comes. Here is the Regex which is performing your reqt. let me know if you have any question.

Regex: '.*(?=\?)'

Here,
.* will pull everything.
(?=) is a positive look ahead
\ escape character for question mark symbol. As question mark symbol is Quantifier in Regex.

python capture from regex

4 Answers4