Remove all the lines that contain the character 'a' in a file and write it to another file

import os

def remove_a():
    f1 = open('test.txt', 'r')
    f2 = open('test2.txt', 'w')
    for line in f1.readlines():
        if 'a' not in line:
            f2.write(line)

    f1.close()
    f2.close()

remove_a()