weird text blend procedure

blend.py

import sys
import random

lines = list()

for line in sys.stdin:
  line = line.strip()
  lines.append(line)

for i, line in enumerate(lines):
  if len(line) == 0:
    print ""
  else:
    char_list = list(line)
    for pos in range(0, i, 2):
      char_list[pos], char_list[pos+1] = char_list[pos+1], char_list[pos]
      char_list[-(pos+1)], char_list[-(pos+2)] = char_list[-(pos+2)], char_list[-(pos+1)]
      #print str(pos) + " " + str(i) + " " + ''.join(char_list)
    print ''.join(char_list)