How to parse sub string and get the digit after the substring in python

Question

I want to fetch the digit of the last occurance of the substring

input : "abc1  foo barabc2 abc3 abc4 foobar"
output : 4

use `split` to split it into substrings, iterate through backwords, checking `substring[-1]` to see if it `isdigit()`. If so, punch out, you're done. — Gillespie, Feb 06 '18 at 15:39
Possible duplicate of [Python 3 Finding the last number in a string](https://stackoverflow.com/questions/17007257/python-3-finding-the-last-number-in-a-string) — ctwheels, Feb 06 '18 at 15:42
@RohanNagalkar this will only work if all your digits are preceded by the string "abc" which is not what you ask in your question — Sembei Norimaki, Feb 06 '18 at 15:52

score 3 · Answer 1 · answered Feb 06 '18 at 15:39

3

You can use re.findall:

import re
s = "abc1  foo barabc2 abc3 abc4 foobar"
print(re.findall('\d+', s)[-1])

Output:

answered Feb 06 '18 at 15:39

Ajax1234

score 1 · Answer 2 · answered Feb 06 '18 at 15:39

1

Well if that's the only thing you want to get then I wouldn't use regexp at all, instead:

s = "abc1 foo barabc2 abc3 abc4 foobar"
print([c for c in s if c.isdigit()][-1])

I hope you were looking for something like that.

answered Feb 06 '18 at 15:39

Szabolcs

1

Wow, that will create a whole list with all the digits and at the end only display the last one. It will work but it will be extremely inefficient (imagine a list of one million elements, all of them digits). If you want to use loops, just reverse iterate until the first digit is found and stop there. – Sembei Norimaki Feb 06 '18 at 15:40
@SembeiNorimaki inefficient compared to what, in what context? Compared it to regular expressions? What if I say, that it's meant to be functional programming instead of imperative style? – Szabolcs Feb 06 '18 at 15:46
If your list has thousand million elements and the last element is a digit, reverse looping will only take one operation. You code will first create a new list of up to thousand million elements (in the case all elements are actually digits) and then just displaying the last one. Inefficient compared to this! – Sembei Norimaki Feb 06 '18 at 15:48
@SembeiNorimaki Obviously. But then why not commented on the regexp solutions? And still, efficiency was not a requirement at all here. – Szabolcs Feb 07 '18 at 08:25

2 Answers2