import re
from pathlib import *

directory = Path("/test")
pattern = r"^file([0-9]+).log$"

next_log_num = 1

for f in directory.iterdir():
    m = re.match(pattern, f.name)

    if m:
        file_num = int(m.group(1))

        if file_num >= next_log_num:
            next_log_num = file_num + 1

print(next_log_num)