https://gist.github.com/00111000/b835c6391772182295ed75822f2ab12f without list comprehensions

foo.py

your_list = 'abcdefghijklmnopqrstuvwxyz
complete_list = []
for current in range(3):
  a = []
  b = []
  for i in your_list:
    a.append(i)
  for y in range(current):
    for i in your_list:
      for x in a:
        b.append(x + i)
  complete_list += b