Return first non-repeating (unique) symbol in the string. With tests and timeit.

first_uniq.py

#!/usr/bin/env python
import re
from timeit import timeit
import unittest

UNIQ_RE = re.compile(r'(.)(?=.*?\1)')

TESTS = {
    'test': 'e',
    'plperl': 'e',
    "Speed is the essence of war. Take advantage of the enemy's " \
    "unpreparedness; travel by unexpected routes and strike him where " \
    "he has taken no precautions. // from Sun Tzu, The Art of War": 'g',
}

TIMEIT_PREPARE = 'from __main__ import TESTS, nonRepeated, first_uniq;' \
                 'input = TESTS.keys()[2]'


class TestFunctions(unittest.TestCase):
    def test_non_repeated(self):
        for test, result in TESTS.iteritems():
            self.assertEqual(nonRepeated(test), result)

    def test_first_uniq(self):
        for test, result in TESTS.iteritems():
            self.assertEqual(first_uniq(test), result)


def nonRepeated(st):
    repeated = dict()
    for l in st:
        if l in repeated: repeated[l] = 0
        else: repeated[l] = 1
    for l in st:
        if repeated[l]: return l


def first_uniq(text):
    reject = set(re.findall(UNIQ_RE, text))
    iterator = (c for c in text if c not in reject)
    return next(iterator, '')


if __name__ == '__main__':
    # unittest.main()
    print timeit('nonRepeated(input)', TIMEIT_PREPARE)
    print timeit('first_uniq(input)', TIMEIT_PREPARE)

Elegant but not very efficient solution (twice as slower as nonRepeated()):

from collections import Counter, OrderedDict

class OrderedCounter(Counter, OrderedDict):
    pass

def unique(string):
    return (char for char, count in OrderedCounter(string).items() if count == 1)

def first_unique(s):
    return next(unique(s), "")