import os, re
files = ['folder/10204_09-03-2021.pdf', 'folder/04_09-03-2021.pdf']
rx = re.compile(r'^[0-9]+_[0-3]?[0-9]-[0-3]?[0-9]-(?:[0-9]{2})?[0-9]{2}\.pdf$', re.I)
for file in files:
if rx.match(os.path.basename(file)):
print(file)
aW1wb3J0IG9zLCByZQpmaWxlcyA9IFsnZm9sZGVyLzEwMjA0XzA5LTAzLTIwMjEucGRmJywgJ2ZvbGRlci8wNF8wOS0wMy0yMDIxLnBkZiddCnJ4ID0gcmUuY29tcGlsZShyJ15bMC05XStfWzAtM10/WzAtOV0tWzAtM10/WzAtOV0tKD86WzAtOV17Mn0pP1swLTldezJ9XC5wZGYkJywgcmUuSSkKZm9yIGZpbGUgaW4gZmlsZXM6CglpZiByeC5tYXRjaChvcy5wYXRoLmJhc2VuYW1lKGZpbGUpKToKCQlwcmludChmaWxlKQoJ