#import sys
import re

String = "1rrtrn2rrn3rrrrnrnr4nr"
splitString = String.split('n')
replacedStrings = []
i=0

for oneString in splitString:
    #oneString = oneString.replace(r'^(.?)*(\[^n])+(.?)*$', "")
    oneString = re.sub(r'^(.?)*(\[^n])+(.?)*$', "", oneString)
    print(oneString)
    replacedStrings.insert(i, oneString)

    i += 1

print(replacedStrings)

1
2
3

4

['1rrtr', '2rr', '3rrrr', 'r', 'r4', 'r']