Thanks for your review Eric.

test_delitem_2 was not added because it fails in just added TestCase for COrderedDict subclass. Added tests for direct calls of other dict methods as Eric suggested.

During writing new tests for direct calls of other dict methods I found yet one bug. Following code makes Python to hang and eat memory.

from collections import OrderedDict
od = OrderedDict()
for i in range(10):
    od[str(i)] = i

for i in range(9):
    dict.__delitem__(od, str(i))

list(od)