FAQ: Introduction to Regular Expressions - Quantifiers - Optional

This community-built FAQ covers the “Quantifiers - Optional” exercise from the lesson “Introduction to Regular Expressions”.

Paths and Courses
This exercise can be found in the following Codecademy content:

Introduction to Regular Expressions
Natural Language Processing
Practical Data Cleaning

FAQs on the exercise Quantifiers - Optional

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The Learn section states:
The regex The monkey ate a (rotten)? banana will completely match both The monkey ate a rotten banana and The monkey ate a banana .

Why does it match The monkey ate a banana instead of The monkey ate a banana with two whitespaces? Wouldn’t the ? symbol only match the text in the parentheses (rotten)? leaving a white space to the right and left?

EDIT: I am now noticing that Codecademy will not format two white spaces in a row, and will instead display it as one. So is the above issue a visual error or does regex actually only match one whitespace?

4 Likes

Hmm. I think you’re right that there would be two whitespaces in the original search string should the group not match: r'The monkey ate a__banana which would therefore not match ‘the monkey ate a banana’.

No idea if the original technically had two spaces and some html fooey (or whatever it is that ignores multiple spaces) ignored it, but it’s certainly not clear to users. I think this should be raised as an error, ta.

2 Likes

Hey there @czjlee! :grinning:

Very good catch there, thank you for posting this!

I just reported it to Codecademy and will let you know when I hear back.

1 Like

The text has been changed to:
The monkey ate a (rotten )?banana

So as to match both expressions

Thanks again for reporting this :slightly_smiling_face:

1 Like

How does this make sense? The lesson very clearly states that regex ranges are greedy and will only return a match for the largest possible quantity, but then in the exercise, it returns matches for multiple quantities in the range.
regexrange1

regexrange2