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()) 33
