Python Challenge #2
===================

URL: http://www.pythonchallenge.com/pc/def/ocr.html

Image of open book with blur texts.
Caption: recognize the characters. maybe they are in the book, 
but MAYBE they are in the page source.

Page Source: Message to "Find rare characters in the mess below" and then a jumble of characters. 

Solution:

To extra data:

import urllib
lines = urllib.open(r'http://www.pythonchallenge.com/pc/def/ocr.html').readlines()
input = ''.join(lines[37:-2])

Counting the number of occurrences of each character in string input, shows that a few alphabets occur 1 time only. But which order are they in?

dct = {}
order = []
for a in input:
    if not a in dct:
        dct[a] = 0
        order.append(a)
    dct[a] += 1


The order in the dict (or a set if used) would be inpredictable. To get the right order, by order of occurrence, compare by position in the list order:

''.join(sorted([c for c in dct if dct[c] == 1], cmp=lambda x,y: order.index(x) - order.index(y)))

gives ==>

equality

URL:

http://www.pythonchallenge.com/pc/def/equality.html