Python - Replace text before first occurrence of string?

Asked Jun 29 '17 at 22:00

Active Jun 29 '17 at 22:00

Viewed 510 times

So if I have a string like:

plz_work = "text I want to get rid of HELLO want to keep this text HELLO want to keep this text"

I want to remove all the text before the first instance of HELLO, like the following:

"HELLO want to keep this text HELLO want to keep this text"

In this case, I used regex, and tried the following off of this and this:

 re.sub(r'.*HELLO','HELLO',plz_work,1)

But I get this:

'HELLO want to keep this text'

Why does this happen? I thought the last parameter signified count and means that it would only perform 1 substitution... why is it going wrong here? Any help would be greatly appreciated, thanks!!

asked Jun 29 '17 at 22:00

ocean800

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All correct except `.*`: [use `r'.*?HELLO'`](http://ideone.com/LVUnMB) – Wiktor Stribiżew Jun 29 '17 at 22:05
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`*` is for greedy repetition. It matches as much of the prior pattern as possible. `*?` is non-greedy. It matches as little as possible. – Steven Rumbalski Jun 29 '17 at 22:06
@StevenRumbalski Ahhhh I see so it matched `text I want to get rid of HELLO want to keep this text HELLO` as the first possible substitution, so it didn't matter that I set the count to 1? – ocean800 Jun 29 '17 at 22:07
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@ocean800: Exactly. – Steven Rumbalski Jun 29 '17 at 22:08
@StevenRumbalski Thanks! :) – ocean800 Jun 29 '17 at 22:09
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Another option is to use non-greedy matching with a lookahead assertion: `re.sub(r'.*?(?=HELLO)', '', plz_work, 1)` – Steven Rumbalski Jun 29 '17 at 22:25
@StevenRumbalski I see.. thanks! Hmm I guess another question, I don't specifically need the `r'` flag, correct? Because there aren't any `\\` 's in my pattern? – ocean800 Jun 29 '17 at 23:02

Python - Replace text before first occurrence of string?

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