Sliding window uniq...

uniq.py

#!/usr/bin/env python

import collections
import sys

MAX_SIZE = 50


if __name__ == '__main__':
    d = collections.OrderedDict()
    for line in sys.stdin:
        if line not in d:
            print(line, end='', flush=True)
            if len(d) >= MAX_SIZE:
                d.popitem()
            d[line] = True