"""

gc.get_referrers() can be used to see objects before they are fully built.

Note that this is only an example.  There are many ways to crash Python

by using gc.get_referrers(), as well as many extension modules (even

when they are using perfectly documented patterns to build objects).

Identifying and removing all places that expose to the GC a

partially-built object is a long-term project.  A patch was proposed on

SF specifically for this example but I consider fixing just this single

example a bit pointless (#1517042).

A fix would include a whole-scale code review, possibly with an API

change to decouple object creation and GC registration, and according

fixes to the documentation for extension module writers.  It's unlikely

to happen, though.  So this is currently classified as

"gc.get_referrers() is dangerous, use only for debugging".

"""

import gc

def g():

    marker = object()

    yield marker

    # now the marker is in the tuple being constructed

    [tup] = [x for x in gc.get_referrers(marker) if type(x) is tuple]

    print tup

    print tup[1]

tuple(g())