`_objects` attribute of ctypes data instances is sometimes not None or a dictionary

Documentation

According to the current ctypes docs, the _objects attribute of ctypes data instances is supposed to be either None or a dictionary:

_objects
This member is either None or a dictionary containing Python objects that need to be kept alive so that the memory block contents is kept valid. This object is only exposed for debugging; never modify the contents of this dictionary.

However, instances created with from_buffer have this attribute set to a memoryview of the source buffer, not to a dictionary:

>>> import ctypes
>>> x = ctypes.c_uint8.from_buffer(bytearray(1), 0)
>>> type(x._objects)
<class 'memoryview'>

This behavior traces to this call of KeepRef inside CDataType_from_buffer_impl. Prior to this call, the result's b_objects is NULL, so this branch in KeepRef is taken, setting b_objects to reference the memoryview.

I'm not familiar with ctypes internals, but to my reading this behavior seems intentional and doesn't appear to cause any problems. Hence I'm filing this as a docs issue.

Bắt đầu với tài liệu về _CData._objects và mã CDataType_from_buffer_impl cùng KeepRef được tham chiếu trong đó tại Modules/_ctypes/_ctypes.c. Xác nhận xem hành vi bộ nhớ của from_buffer với memoryview có phải là chủ ý hay không, sau đó cập nhật tài liệu để mô tả chính xác hành vi này; kiểm tra hành vi được tài liệu hóa bằng ví dụ ctypes được cung cấp.