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(B5) this is an old issue that was forgotten twice on the
 issue tracker: ``class C: __new__=int.__new__`` and ``class C(int):
 __new__=object.__new__`` can each be instantiated, even though they
 shouldn't. This is because ``__new__`` is completely ignored if it is
 set to any built-in function that uses ``tp_new_wrapper`` as its C code
 (many of the built-in types' ``__new__`` are like that).
 http://bugs.python.org/issue1694663#msg75957,
 http://bugs.python.org/issue5322#msg84112. In (at least) CPython 3.5,
 a few classes work only thanks to abuse of this bug: for example,
 ``io.UnsupportedOperation.__new__(io.UnsupportedOperation)`` doesn't
 work, but that was not noticed because ``io.UnsupportedOperation()``
 mistakenly works.