gistfile1.py

import uuid
import random

def ordered_uniquification(items):
    seen = set()
    for item in items:
        if not item in seen:
            seen.add(item)
            yield item

if __name__ == '__main__':
    total = 100000

    original_emails = [str(uuid.uuid1()) + '@example.com'
                       for _ in range(int(total / 2))] # Should be xrange in Python 2.*

    emails = original_emails * 2
    random.shuffle(emails)

    unique_emails = list(ordered_uniquification(emails))

    assert len(unique_emails) == len(original_emails)

    # A far less efficient one-liner that basically does the same thing
    # (don't worry, I don't normally write code like this lol)
    assert unique_emails == [email for _, email in
                             sorted((index, email)
                                    for email, index in
                                    {email: i
                                     for i, email in reversed(list(enumerate(emails)))}.items())]