Python Challenge level 18: “can you tell the difference?”

Level 18 is imaginative again.

Hint 1: it is more obvious that what you might think.

Fact 1: the main difference between images is brightness, we’ll go to brightness.html which is an almost twin page except for a new hint.

Hint 2: maybe consider deltas.gz.

After retrieving deltas.gz, we can go on with the script:

import gzip,difflib
deltas=gzip.GzipFile('deltas.gz', 'rb').read()
deltas=deltas.splitlines()
left,right,png=[],[],['','','']
for row in deltas:
    left.append(row[:53])
    right.append(row[56:])
diff = list(difflib.ndiff(left,right))

for row in diff:
    bytes = [chr(int(byte,16)) for byte in row[2:].split()]
    if row[0]=='-': png[0]+=''.join(bytes)
    elif row[0]=='+': png[1]+=''.join(bytes)
    elif row[0]==' ': png[2]+=''.join(bytes)

for i in range(3):
    open('18_%d.png' %i,'wb').write(png[i])

The images created show the following texts:

18_0.png: fly
18_1.png: butter
18_2.png: ../hex/bin.html

That’s that. As allways, once you figure out the module you should be using makes the solution pretty straight forward. Level 19 is next.