How to check if a line contains a string in Python

Question

I'm trying to check if a subString exists in a string using regular expression.

RE : re_string_literal = '^"[a-zA-Z0-9_ ]+"$'

The thing is, I don't want to match any substring. I'm reading data from a file:

Now one of the lines have this text: cout<<"Hello"<<endl;

I just want to check if there's a string inside the line and if yes, store it in a list.

I have tried the re.match method but it only works if we have to match a pattern, but in this case, I just want to check if a string exists or not, if yes, store it somewhere.

re_string_lit = '^"[a-zA-Z0-9_ ]+"$'

text = 'cout<<"Hello World!"<<endl;'

re.match(re_string_lit,text)

It doesn't output anything.

In simple words, I just want to extract everything inside ""

re.match works just fine for this, but you have not shown any code. Provide a minimal reproducible example. — zvone
– zvone, Commented Jan 8, 2021 at 16:48
What do you mean if a string exists or not? It is a string... To check if it's not empty you can do if s.strip(): — Tomerikoo
– Tomerikoo, Commented Jan 8, 2021 at 16:49
@chepner not accurate. re.match only matches from the start of the string. re.search will look everywhere... — Tomerikoo
– Tomerikoo, Commented Jan 8, 2021 at 16:52
One of your examples has a ! in the input string, which is not part of your regular expression. You might want to use [^"] rather than trying to enumerate all allowed characters, but then you need to address the issue of a string like "foo\"bar". — chepner
– chepner, Commented Jan 8, 2021 at 16:54
@QasimKhan What about quotes inside comments? Do you want actual C++ strings, or just anything that's surrounded by quotes? — ekhumoro
– ekhumoro, Commented Jan 8, 2021 at 17:01

Aadesh Dhakal · Accepted Answer · 2021-01-08 17:09:54Z

1

If you just want to extract everything inside "" then string splitting would be much simpler way of doing things.

>>> a = 'something<<"actualString">>something,else'
>>> b = a.split('"')[1]
>>> b
'actualString'

The above example would only work for not more than 2 instances of double quotes ("), but you could make it work by iterating over every substring extracted using split method and applying a much simpler Regular Expression.

answered Jan 8, 2021 at 17:09

Aadesh Dhakal

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Comments

Qasim Khan · Accepted Answer · 2021-01-08 17:01:25Z

0

This worked for me:


re.search('"(.+?)"', 'cout<<"Hello"<<endl')

answered Jan 8, 2021 at 17:01

Qasim Khan

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4 Comments

Tomerikoo Over a year ago

"([^"]+)" is a bit more efficient than a lazy quantifier on .

Qasim Khan Over a year ago

@Tomerikoo Thankyou so much. Is there a way to access this substring after performing the search method?

Tomerikoo Over a year ago

Yes. it is stored in group 1. So, match = re.search('"(.+?)"', 'cout<<"Hello"<<endl') and the string is match.group(1). If you want it with the quotes, then it's group(0) or just group()

Qasim Khan Over a year ago

@Tomerikoo Thank you so much!

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