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Currently bool(None) returns False only because it has a special case in PyObject_IsTrue(). All other types can become False only if they implement __bool__() or __len__().
I propose removing the special case branch and instead adding __bool__ to None. This will simplify the explanation of what bool() does to: "bool(x) always returns True unless the object defines __bool__() to return False or defines __len__() to return a non-zero value".
The removal of the special case will slightly slow down tests for "if None", and it will slightly speed-up tests for "if x" where x is something other than True, False, or None.