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In python 2.7, ABCs's caches and registries are sets. But in python 3.6 they are WeakSet. In consequence, the output of _dump_registry() is almost useless:
from collections import abc abc.Iterator._dump_registry() Class: collections.abc.Iterator Inv.counter: 40 _abc_cache: <_weakrefset.WeakSet object at 0x7f4b58fe2668> _abc_negative_cache: <_weakrefset.WeakSet object at 0x7f4b53283780> _abc_negative_cache_version: 40 _abc_registry: <_weakrefset.WeakSet object at 0x7f4b58fe2630>
We could convert them into a regular set before printing: if isinstance(value, WeakSet): value = set(value) The result:
abc.Iterator._dump_registry() Class: collections.abc.Iterator Inv.counter: 40 _abc_cache: {<class 'dict_valueiterator'>, <class 'bytearray_iterator'>, <class 'tuple_iterator'>, <class 'dict_itemiterator'>, <class 'dict_keyiterator'>, <class 'str_iterator'>, <class 'zip'>, <class 'set_iterator'>, <class 'list_reverseiterator'>, <class 'range_iterator'>, <class 'longrange_iterator'>, <class 'list_iterator'>, <class 'bytes_iterator'>} _abc_negative_cache: set() _abc_negative_cache_version: 40 _abc_registry: set()
NB: It seems pretty weird to me that registry is empty... All the iterators in the cache should've been in the registry instead, should'nt they?