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 How would I get everything before a : in a string Python — Dani Mesejo
– Dani Mesejo, Commented Jan 4, 2019 at 19:40

Amit Amola · Accepted Answer · 2019-01-04 19:54:45Z

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 4, 2019 at 19:54

answered Jan 4, 2019 at 19:43

Amit Amola

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4 Comments

user3525290 Over a year ago

I wanted to get better with regexpressions.

Amit Amola Over a year ago

Oh, I see, okay, give me a minute, I'll make edits and get back with regex answer.

user3525290 Over a year ago

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)

Jan Over a year ago

Get rid of the backslash in square brackets.

Jan · Accepted Answer · 2019-01-04 19:51:43Z

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 4, 2019 at 19:51

Jan

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user3525290 Over a year ago

Thanks everyone for all of the help

mad_ · Accepted Answer · 2019-01-04 19:55:34Z

1

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 4, 2019 at 19:55

mad_

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Deep · Accepted Answer · 2019-01-04 19:57:44Z

1

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.

answered Jan 4, 2019 at 19:57

Deep

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