Python Challenge level 18

http://www.pythonchallenge.com/pc/return/balloons.html (logib:huge/file)

- Two picture, one is brighter. "Can you tell the difference?" and a comment says it's more easy than I think.
- Just visit http://www.pythonchallenge.com/pc/return/brightness.html and you will see the same page.....wait! The comment changes..."maybe consider deltas.gz"!
- Download "deltas.gz" from http://www.pythonchallenge.com/pc/return/deltas.gz and extract delta.txt.
- Two similar data sets showed in this file. Both of them start with "89 50 4E 47 0D ..."
- According to https://en.wikipedia.org/wiki/List_of_file_signatures, "89 50 4E 47 0D 0A 1A 0A" is a hex signature of PNG file!

- We should "tell the difference" of these two data set. A simple and easy way is use difflib.

- See also: https://docs.python.org/2/library/difflib.html

import difflib

f = open("delta.txt")
left_data = []
right_data = []


for line in f:
 left_data.append(line[0:len(line)/2].strip())
 right_data.append(line[len(line)/2:len(line)].strip())
 if left_data[-1] == "": left_data.pop()
 if right_data[-1] == "": right_data.pop()

f.close()

diff = list(difflib.ndiff(left_data, right_data))

diff_space = []
diff_plus = []
diff_minus = []

for i in diff:
 if i[0] == " ": diff_space.extend(i[2:].split())
 elif i[0] == "+": diff_plus.extend(i[2:].split())
 elif i[0] == "-": diff_minus.extend(i[2:].split())

space = open("space.png", "wb")
plus = open("plus.png", "wb")
minus = open("minus.png", "wb")

for i in diff_space:
 space.write(chr(int(i, 16)))
for i in diff_plus:
 plus.write(chr(int(i, 16)))
for i in diff_minus:
 minus.write(chr(int(i, 16))) 
 
space.close()
plus.close()
minus.close()

- The three result pictures are look like:

- The next level is http://www.pythonchallenge.com/pc/hex/bin.html, username and password are "butter" and "fly".