How to get % similarity between strains and mutation files

I’m very new to python, and having some difficulty getting hang of some more complicated things

I have multiple files which look like so:

hCoV-19/Singapore/4/2020|EPI_ISL_410535|2020-02-03

hCoV-19/USA/WA13-UW9/2020|EPI_ISL_413601|2020-03-02

hCoV-19/USA/WA-UW142/2020|EPI_ISL_416680|2020-03-11

Please be aware that the lines above are meant to be one file

I want to extract the EPI_ISL_000000 for an easy comparison among files.

Could someone please advise on:

1. A programme to extract this data into new files (There’s many lines in each file – 1000+)

2. A programme to then give a % comparison between two or more files – comparing all lines in one file against all lines in a second+ file

   left_lineagelist = [x.split('_')[-1].split('|')[0] 
                          for x in left_lineagelist]
        right_lineagelist = set([x.split('_')[-1].split('|')[0] 
                          for x in right_lineagelist])

for line in lines:
    if line[0] == '>':
        print(line[1:])