Regular expression to get substring from a string

Question

consider I have a string as following,

\n this is a paragraph. please ignore  \n this is a only for testing. please ignore \n

I have a search word as "only for testing". and I want to get the sentence which contains "only for testing" with in the \n the search word resides. In this case the output will be this is a only for testing. please ignore.

If I give paragraph as search word I should get the output as

this is a paragraph. please ignore

I have tried

test_str = "\\n this is a paragraph. please ignore  \\n this is a only for testing. please ignore \\n"
pattern = re.compile("\\\\n(.+?)\\\\n")
match = pattern.findall(test_str)

But not working as expected

`print ([sent for sent in test_str.split("\\n") if 'only for testing' in sent])` ([demo](https://rextester.com/RKBQ77131)) — Wiktor Stribiżew, Dec 12 '19 at 12:57
If you're insisting on a Regex solution then you need to escape your search term for use in regex and then interpolate that string within `(.+?)` — MonkeyZeus, Dec 12 '19 at 13:00
You should Google the steps I mentioned individually. Here's a start, https://stackoverflow.com/q/280435/2191572. Are you new to Python too? — MonkeyZeus, Dec 12 '19 at 13:05
With regex, it will be a pain, see `re.findall(r'(?:^|\\n)((?:(?!\\n).)*only for testing(?:(?!\\n).)*)', test_str)` [demo](https://rextester.com/JISY46794) — Wiktor Stribiżew, Dec 12 '19 at 13:16
Consider using raw strings (`r"foo"`) to prevent the blackslash plague. There is really no reason not to use raw strings when using regex with python. — Error - Syntactical Remorse, Dec 12 '19 at 13:42
@WiktorStribiżew: Your first answer without using the regex should be good I guess. I will go for that. Thanks a lot Wiktor — ѕтƒ, Dec 17 '19 at 12:53

score 2 · Accepted Answer · answered Dec 17 '19 at 12:54

You may use a solution without a regular expression:

result = [sent for sent in test_str.split("\\n") if 'only for testing' in sent]

See the Python demo

Details

test_str.split("\\n") - split the text by \n
if 'only for testing' in sent - only keep the items that contain only for testing (for a case insensitive comparison, use if 'only for testing' in sent.lower())

Regular expression to get substring from a string

1 Answers1