stable sort in python

test script

from random import choice
from operator import attrgetter

years = range(1992, 1995)
months = range(1, 3)
day = range(1, 3)
idx = range(2)

class A(object):
    def __init__(self):
        self.cat = 'cat%d' % (choice(idx),)
        self.pub = '%s-%02d-%02d' % (choice(years), choice(months), choice(day))

    def __repr__(self):
        return 'A cat: %s pub: %s' % (self.cat, self.pub)

def test1():
    out = [ A() ] * 100 
    s1 = sorted(sorted(out, key=attrgetter('pub'), reverse=True), key=attrgetter('cat'))
    prev = s1[0]
    for i in s1[1:]:
        assert((i.cat > prev.cat) or (i.cat == prev.cat and i.pub <= prev.pub))
        prev = i 

if __name__ == '__main__':
    test1()
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