Python3 regex match timestamp pattern

timestamp_pattern.py

import re
from typing import List, Set

filename = ""
out_filename = ""
records: List[str] = []
ts_pattern = re.compile(r"^.+(\d{2}/\w{3}/\d{4}:\d{2}:\d{2}:\d{2})")
seen: Set[str] = set()


with open(filename) as lines:
    for line in lines:
        m = ts_pattern.match(line)
        if m is not None:
            ts: str = m.group(1)
            if ts in seen:
                records.append(ts)
            else:
                seen.add(ts)

with open(out_filename, mode='wt', encoding='utf-8') as out:
    out.write('\n'.join(records))