import re
lst = ['AB8372943.txt', 'test.pdf', '123485940.docx', 'CW2839502.txt', 'AB1234567.txt', '283AB.txt']
lst2 = [s for s in lst if re.match(r"AB\d{7}\.txt\Z", s)]
print(lst2)
aW1wb3J0IHJlCgpsc3QgPSBbJ0FCODM3Mjk0My50eHQnLCAndGVzdC5wZGYnLCAnMTIzNDg1OTQwLmRvY3gnLCAnQ1cyODM5NTAyLnR4dCcsICdBQjEyMzQ1NjcudHh0JywgJzI4M0FCLnR4dCddCmxzdDIgPSBbcyBmb3IgcyBpbiBsc3QgaWYgcmUubWF0Y2gociJBQlxkezd9XC50eHRcWiIsIHMpXQpwcmludChsc3QyKQ==