Pick the filename with the largest <a> value from files like "file_<a>.<b>.npy.gz"

max_a_filename.py

import os
import re

re_pattern = r'file_(?P<a>[0-9]*)\.[0-9]*\.npy\.gz'

filenames = os.listdir('.')
matches = [re.match(re_pattern, filename) for filename in filenames]
matches = [match for match in matches if match]
max_a_match = max(matches, key=lambda x: int(x.groupdict()['a']))
max_a_filename = max_a_match.group()
print(max_a_filename)