Mini-script to parse my read-books file

parse-read-books.py

with open('books.txt') as f_old, open('newbook.txt', 'w+') as f_new:
  for line in f_old:
    if "[" in line and "]" in line:
      # Process the line only if it has the "[" and "]" characters
      book_name, sep1, old_date_str = line.partition("[")
      _, _, book_name = book_name.partition("-")

      month, _, tmp = old_date_str.partition("/")
      day, _, tmp = tmp.partition("/")
      year, _, _ = tmp.partition("]")

      if len(day) == 1:
        day = "0" + day

      if len(month) == 1:
        month = "0" + month

      if len(year) == 2:
        year = "20" + year

      # String is: "- [YYYY-mm-dd] <Book Name>"
      new_line = "- " + "[" + year + "-" + month + "-" + day + "] " + book_name + "\n";
      f_new.write(new_line)
    else:
      f_new.write(line)