regex to match repeating string python

Question

I got strings which go:

abc123abc123abc123

abc123

abc123abc123abc123abc123abc123abc123

etc (varying units of abc123 which I don't know the length of repeat)

The task is to extract the first 1 and first a and the last c and last 3. Is it possible to do it with 1 regex and how exactly if it is possible? I kept count of the repeating units and based on the count I have been able to perform the task with a few regex, but would like to use one regex if possible. Thanks

Edit: In the real situation. It is more like a:(a number)bc:(a number)1:(a number)23:(a number) etc and I have to capture the first a number, the first 1 number, the last c number and the last 3 number.

Jeff

I don't quite understand. Do you want to find their positions? Because if you "extract" them, how does the first a differ from any other one? — Martin Ender
– Martin Ender, Commented Oct 29, 2012 at 0:19
In your examples, the first a is always at the start, the first 1 is always the fourth charachter, the last c is always the fourth from the rigth and the last c is the last character. So why dou you need a regex instead of x[0], x[3], x[-4] and x[-1]? — Sebastian
– Sebastian, Commented Oct 29, 2012 at 0:23
Yeah, please clarify your question a bit (with expected inputs -> outputs, and strings expected to not match (if any)..) — redShadow
– redShadow, Commented Oct 29, 2012 at 0:29

Hans Then · Accepted Answer · 2012-10-29 00:30:27Z

3

This is easiest done using two regexen. "^(a)bc(1)23" and "ab(c)12(3)$". It may be possible to merge these two, but the regular expression will get pretty unreadable.

answered Oct 29, 2012 at 0:30

Hans Then

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2 Comments

Martin Ender Over a year ago

I don't see the purpose of this? If the OP knows his string is a repetition of abc123 then your regexes will invariably return a, 1, c and 3.

Hans Then Over a year ago

I modelled the answer after the edit by OP. My example was not intended to be literal code, but to match the question of the OP.

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