Find the latest version of strings - Python

Question

Trying to find the latest version of a list of strings. For example,

"01022021_1"
"01032021_1"
"02032021_1"
"02032021_2"

The most recent is going to be the last one, but how can I use regex to take those strings and pick out the latest dated and versioned name?

So these are dates with a version number.

Do you have to use a regex? If they're all padded to the same length and the years don't change, you can use the inbuilt `max()`: `max(["01022021_1", "01032021_1", "02032021_1", "02032021_2"])` gives `'02032021_2'` — Pranav Hosangadi, Jul 15 '21 at 15:29
would this simply work if the years change as not_speshal said? — caasswa, Jul 15 '21 at 15:32
@Epsi95 That won't work because it will put March 2020 ahead of January 2021. — Barmar, Jul 15 '21 at 15:32
@caasswa yes. Barmar gives a more robust solution in their answer — Pranav Hosangadi, Jul 15 '21 at 15:32

Barmar · Accepted Answer · 2021-07-15T15:36:26.300

8

Use max() with a key that extracts and reorders the parts of the string so the year is most significant.

max(yourList, key = lambda s: (s[4:8], s[:4], int(s[8:])))
#                              YYYY    MMDD   VERSION

edited Jul 15 '21 at 15:36

answered Jul 15 '21 at 15:31

Barmar

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Hey Barmar, could you explain this a bit more? not sure i understand the 4:8 4 and 8 part – caasswa Jul 15 '21 at 15:35
That's slice notation, it should be familiar to most Python programmers. See https://stackoverflow.com/questions/509211/understanding-slice-notation – Barmar Jul 15 '21 at 15:37
oh wait this is just substringing isn't it – caasswa Jul 15 '21 at 15:37
sorry i'm a bit of a noob with python, i'm a C#/C++ programmer so didn't recognise it. Thanks man! – caasswa Jul 15 '21 at 15:37

score 0 · Answer 2 · answered Jul 15 '21 at 15:31

0

If you can guarantee the format of your strings (that is (I think), DDMMYYYY_v, where v is version), then you could use max(), as has been suggested in the comments.

answered Jul 15 '21 at 15:31

Blair Nangle

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score 0 · Answer 3 · answered Jul 15 '21 at 15:42

0

if it's a list of strings, and the last element in the list is always the latest, the simplest would be the following:

stringlist = [
    "01022021_1",
    "01032021_1",
    "02032021_1",
    "02032021_2"]

latest = stringlist[-1]
print(latest)

# output:
# 02032021_2

List handling is extremely easy in python. Using a negative number means you start counting from the end of the list.

answered Jul 15 '21 at 15:42

Edo Akse

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unfortunately. the string is not ordered by default. – Lei Yang Jul 15 '21 at 15:47
that doesn't matter though, as the OP states *The most recent is going to be the last one,* – Edo Akse Jul 15 '21 at 15:54
by recent, he probably means recent by time, not by literal order. – Lei Yang Jul 15 '21 at 15:55
if that's the case, then the excellent answer from Barmar is the best – Edo Akse Jul 15 '21 at 15:57

Find the latest version of strings - Python

3 Answers3