copy.copy() of a collections.deque subclass, and both copy.copy() and copy.deepcopy() of an array.array subclass, dropped the instance __dict__. For array the result was also a plain array rather than the subclass. pickle and the list/dict/set subclasses don't have this problem, so the behavior was inconsistent.

>>> import copy
>>> from collections import deque
>>> class D(deque): pass
>>> d = D([1, 2, 3]); d.label = "kept"
>>> copy.copy(d).label          # was AttributeError
'kept'
>>> from array import array
>>> class A(array): pass
>>> a = A("i", [1, 2]); a.tag = "kept"
>>> copy.copy(a).tag, type(copy.copy(a)) is A   # was AttributeError, base array
('kept', True)

deque.__copy__ (shared with deque.copy()) now copies the instance __dict__ onto the new object. array.__copy__/__deepcopy__ now build the actual subclass and copy the __dict__ — shallow for __copy__, deep (via the memo) for __deepcopy__, registering the new object in the memo first so self-referential attributes don't recurse forever.

Both types' __reduce_ex__ already carried this state, which is why pickle (and deepcopy of a deque, which has no __deepcopy__) were already correct.

Fixes #152042.

• Issue: copy.copy()/copy.deepcopy() of deque and array subclasses drop instance attributes (array also changes type) #152042