AppPkg/Applications/Python/Python-2.7.2/Lib/test/crashers/loosing_mro_ref.py

   1 """
   2 There is a way to put keys of any type in a type's dictionary.
   3 I think this allows various kinds of crashes, but so far I have only
   4 found a convoluted attack of _PyType_Lookup(), which uses the mro of the
   5 type without holding a strong reference to it.  Probably works with
   6 super.__getattribute__() too, which uses the same kind of code.
   7 """
   8
   9 class 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
  24 class Base(object):
  25     mykey = 'from Base'
  26
  27 class 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 :-)
  32 X = type('X', (Base,), {MyKey(): 5})
  33
  34 print X.mykey
  35 # I get a segfault, or a slightly wrong assertion error in a debug build.