How to regex a version number in python?

Question

In python 3.6 I want to match a version number, i.e. a string that contains numbers and dots.

Here is what I have tried:

re.search(r"([\d\.+]+)", str)

but this also matches str="2020" which obviously does not contain a dot. Although I require at least one dot to match! Is that a bug or what am I misunderstanding from the documentation about the + sign?

I also tried

re.search(r"(\d+\.+)", "2020.4.3")

which does match, but only returns the string "2020.".

Here are some test cases:

abba -> No match
2020 -> No match
1.1.1.1 -> 1.1.1.1
2020.4.3 -> 2020.4.3

anubhava · Accepted Answer · 2020-07-24T07:44:38.130

1

You can use this regex in python to ensure at least one dot:

r'\b\d+(?:\.\d+)+'

RegEx Demo

RegEx Details:

\b: Word boundary
\d+: Match 1+ digits
(?:\.\d+)+: Match a group 1+ times containing dot followed by 1+ digits

edited Jul 24 '20 at 07:44

answered Jul 24 '20 at 07:42

anubhava

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Does not work for me. When I use `2020.2` as a test string it returns nothing – Alex Jul 24 '20 at 07:44
1

That's not correct, it will return full match. Are you using `findall`? – anubhava Jul 24 '20 at 07:45
2

@Alex You must've done something wrong. Double-check the pattern. Side note: you might want to replace the last `+` with `{1,3}` (or `{0,3}` if you want to also match numbers only without dots). – 41686d6564 stands w. Palestine Jul 24 '20 at 07:45
1

I am using `search`, see question – Alex Jul 24 '20 at 07:45
1

Yes, I did copy it incorrectly. It seems to work, thanks a lot – Alex Jul 24 '20 at 07:46
Indeed `re.search(r'\b\d+(?:\.\d+)+', "2020.2").group(0)` will return `2020.2` – anubhava Jul 24 '20 at 07:47
What does the `?:` do? – Alex Jul 24 '20 at 07:47
`(?:..)` is a non-capturing group so that we don't make unnecessary groups. – anubhava Jul 24 '20 at 07:47
Can you repeat that in english please? – Alex Jul 24 '20 at 07:48
1

@Alex See: [What is a non-capturing group in regular expressions?](https://stackoverflow.com/q/3512471/8967612) – 41686d6564 stands w. Palestine Jul 24 '20 at 07:48
Yes, found it in the docs... – Alex Jul 24 '20 at 07:49
But still unclear to me' – Alex Jul 24 '20 at 07:49
[Rede about non-capturing groups](https://www.regular-expressions.info/brackets.html#:~:text=Non%2DCapturing%20Groups&text=The%20question%20mark%20and%20the,the%20end%20of%20the%20regex.&text=This%20regex%20has%20no%20quantifiers.) – anubhava Jul 24 '20 at 07:50
Sometimes documentation can be more confusing than explanative. As I understand it is used to find a match, but is not 'returned' as a result. No still unclear to me related to my question. So basically I could remove it, then the whole expression is used as a match. Yes ehat I want! But then it is not working anymore – Alex Jul 24 '20 at 07:52
It is working because of `+` after group which makes sure 1 or more occurrence of `.` and digits – anubhava Jul 24 '20 at 07:57
Thanks, that is an expression I can understand now – Alex Jul 24 '20 at 07:58

How to regex a version number in python?

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