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

def remove_a(filename, new_file):
  with open(filename, 'r') as file:
      f1 = file.readlines()
      with open(new_file, 'w') as file1:
          for line in f1:
              if 'a' not in line:
                  file1.write(line)

remove_a('file.txt', 'file1.txt')