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/Lib/test/crashers/loosing_mro_ref.py

http://unladen-swallow.googlecode.com/
Python | 35 lines | 27 code | 1 blank | 7 comment | 0 complexity | a578779515ab3178baaff89e5269806e MD5 | raw file
 1"""
 2There is a way to put keys of any type in a type's dictionary.
 3I think this allows various kinds of crashes, but so far I have only
 4found a convoluted attack of _PyType_Lookup(), which uses the mro of the
 5type without holding a strong reference to it.  Probably works with
 6super.__getattribute__() too, which uses the same kind of code.
 7"""
 8
 9class MyKey(object):
10    def __hash__(self):
11        return hash('mykey')
12
13    def __cmp__(self, other):
14        # the following line decrefs the previous X.__mro__
15        X.__bases__ = (Base2,)
16        # trash all tuples of length 3, to make sure that the items of
17        # the previous X.__mro__ are really garbage
18        z = []
19        for i in range(1000):
20            z.append((i, None, None))
21        return -1
22
23
24class Base(object):
25    mykey = 'from Base'
26
27class Base2(object):
28    mykey = 'from Base2'
29
30# you can't add a non-string key to X.__dict__, but it can be
31# there from the beginning :-)
32X = type('X', (Base,), {MyKey(): 5})
33
34print X.mykey
35# I get a segfault, or a slightly wrong assertion error in a debug build.