Instead to create a script in Python to convert numbers in integers, you can use awk: "python3 parse.py" becomes "awk '{printf "%d\n", $0}'"
The problem seems to boil down to:
"Find all files with the pattern '[something]_data.csv' and report if '[something]_A.csv' doesn't exist"
Unless I'm missing something, all the sorting and sequence generation isn't adding anything.
$ printf '%d\n' "0005"
5 $ echo "0005" | xargs printf '%d\n'
5
That said, my suggestion doesn't work anyway since the leading 0 marks it as octal, d'oh (as mentioned elsewhere in the thread). $ printf '%d\n' "0025"
21