import gc
import time
import weakref


def collect():
    gc.collect()
    time.sleep(0.15)


weakrefs = []
sentinel = []

def watch(obj, kwarg=True):
    assert kwarg is True
    # log the death of the reference by appending to the sentinel
    ref = weakref.ref(obj, sentinel.append)
    weakrefs.append(ref)

assert not sentinel

print 1
thunk1 = lambda: None
watch(thunk1)
assert not sentinel

del thunk1
collect()
assert sentinel

del sentinel[:]

print 2
thunk2 = lambda: None
watch(thunk2, kwarg=True)  # <--- only difference: called with a kwarg
assert not sentinel

del thunk2
collect()
assert sentinel