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

   1 """
   2 gc.get_referrers() can be used to see objects before they are fully built.
   3
   4 Note that this is only an example.  There are many ways to crash Python
   5 by using gc.get_referrers(), as well as many extension modules (even
   6 when they are using perfectly documented patterns to build objects).
   7
   8 Identifying and removing all places that expose to the GC a
   9 partially-built object is a long-term project.  A patch was proposed on
  10 SF specifically for this example but I consider fixing just this single
  11 example a bit pointless (#1517042).
  12
  13 A fix would include a whole-scale code review, possibly with an API
  14 change to decouple object creation and GC registration, and according
  15 fixes to the documentation for extension module writers.  It's unlikely
  16 to happen, though.  So this is currently classified as
  17 "gc.get_referrers() is dangerous, use only for debugging".
  18 """
  19
  20 import gc
  21
  22
  23 def g():
  24     marker = object()
  25     yield marker
  26     # now the marker is in the tuple being constructed
  27     [tup] = [x for x in gc.get_referrers(marker) if type(x) is tuple]
  28     print tup
  29     print tup[1]
  30
  31
  32 tuple(g())