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General Discussion

Posted by Hashim Warren
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Hashim Warren
Front End Web Development Techdegree Student 1,207 Points

REGEX Headache

I'm reading up on regular expressions, and understanding everything, until I hit this:

^ is a line anchor outside a class, but a class metacharacter inside a class (but, only when it is immediately after the class's opening bracket; otherwise, it's not special inside a class)

Boink! My brain twisted, and suddenly I'm lost.

I can't wait until Treehouse tackles regex! You folks will explain it in a way I understand.

1 Answer

Kenneth Love
STAFF
Kenneth Love
Treehouse Guest Teacher
Kenneth Love
Kenneth Love
Treehouse Guest Teacher

So, yes, my course is coming out soon (but it's regex in a Python-centric explanation, of course) and you've been waiting 10 months, but I want to answer this for you anyway.

re.search(r'^Hello', 'Hello there')
'Hello'
re.search(r'^hello', 'Well, hello there')
None

So, outside of a set (where did you find the 'class' name? That's a weird one to me), the ^ means "This is the beginning of the string". The opposite of this, $, means "This is the end of the string".

Now for example #2.

re.search(r'[^2468]+', '0123456789')
'013579'

We're using a set [ ] of characters that we want to match. But since we started the set with a caret, that means "Don't match this set!".

Does that help, 10 months too late (in my defense, I've only been here for about 8 months)?

Hashim Warren
.a{fill-rule:evenodd;}techdegree
Hashim Warren
Front End Web Development Techdegree Student 1,207 Points

Kenneth, thanks! I'm going to tackle this again once your course launches.