Why do I get an extra empty hit when using regex to split a string?

Question

I have a string like this: ape4banana3 and I split it like this:

>>>re.split('([1-5]?)|\s', "ape4banana3")
['ape', '4', 'banana', '3', '']

Why do I get the trailing '' in my result? Can I get rid of it by writing a smarter regex?

Side note: The regex has the alternation because sometimes the string looks like this: ape4 banana3 and then I want to lose the whitespace.

For extra credit: Is there a way I can get this result instead? ['ape4', 'banana3']?

You're splitting on the numbers, so it has to return you the value after the last number, even if it's the empty string. If you don't want that, you can _search_ pairs of non-number then number, instead of splitting. — abarnert, Oct 12 '13 at 00:38
Related: http://stackoverflow.com/questions/3845423/remove-empty-strings-from-a-list-of-strings — luiscubal, Oct 12 '13 at 00:39
For the extra credit, just search (not split) on `'[^1-5]+[1-5]'` — abarnert, Oct 12 '13 at 00:39
(I posted comments rather than answers because I didn't take care of the \s part. Hopefully someone can write a complete answer before I get to a computer.) — abarnert, Oct 12 '13 at 00:40
@Fylke, unrelated to your question, www.mostlyguessing.com, from your profile, is being parked. I'll delete this after you see it — TankorSmash, Oct 12 '13 at 01:10
@user2357112 Because I know that will be at most one number in the string — Fylke, Oct 13 '13 at 23:15

score 4 · Accepted Answer · answered Oct 12 '13 at 00:40

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You're seeing the extra space because you're splitting on digits and so you get the empty string after your last digit.

As to your extra credit, this seems like the easiest solution:

>>> re.findall(r"([a-zA-Z]+[1-5]+)", "ape4banana3")
['ape4', 'banana3']
>>> re.findall(r"([a-zA-Z]+[1-5]+)", "ape4 banana3")
['ape4', 'banana3']

You might need to replace [a-zA-Z] with a more specific or less specific pattern depending on your use case, this regex is only based on the strings you've posted here.

answered Oct 12 '13 at 00:40

Nolen Royalty

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What's the significance of the 'r' before the regex string? – Fylke Oct 12 '13 at 00:42
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@Fylke the `r` marks the string as a [raw string](http://docs.python.org/2/library/re.html#raw-string-notation), which means that you don't need to escape backslashes. It's not technically needed in this case, but I do it out of habit as most regexes end up needing something like a `\d` or `\w` – Nolen Royalty Oct 12 '13 at 00:43
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(although to be honest in this case it's because I'm really lazy and used `\d` to write my solution because it's easier to type and then replaced it with a `[1-5]` after posting :p – Nolen Royalty Oct 12 '13 at 00:47

Neil Neyman · Answer 2 · 2013-10-12T00:48:03.187

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This is because the 3 is splitting banana and an empty strung at the end.

As for the second result, what about can you just splitting on \s?

edit Oh I see, the space is not always there.

You can match like:

 ([A-Za-z].?[1-5])([A-Za-z].?[1-5])

The parentheses are used to put each enclosed section into a group that will be contained as its own array cell.

edited Oct 12 '13 at 00:48

answered Oct 12 '13 at 00:38

Neil Neyman

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I don't just split on \s because the string will just as often contain no whitespace. – Fylke Oct 12 '13 at 00:40

Why do I get an extra empty hit when using regex to split a string?

2 Answers2