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(B7) frame.clear() does not clear f_locals, unlike what a test says
 (Lib/test/test_frame.py)::
 def test_locals_clear_locals(self):
 # Test f_locals before and after clear() (to exercise caching)
 f, outer, inner = self.make_frames()
 outer.f_locals
 inner.f_locals
 outer.clear()
 inner.clear()
 self.assertEqual(outer.f_locals, {})
 self.assertEqual(inner.f_locals, {})
 This test passes, but the C-level PyFrameObject has got a strong
 reference to f_locals, which is only updated (to be empty) if the
 Python code tries to read this attribute. In the normal case,
 code that calls clear() but doesn't read f_locals afterwards will
 still leak everything contained in the C-level f_locals field. This
 can be shown by this failing test::
 import sys
 def g():
 x = 42
 return sys._getframe()
 frame = g()
 d = frame.f_locals
 frame.clear()
 print(d)
 assert d == {} # fails! but 'assert d is frame.f_locals' passes,
 # which shows that this dict is kept alive by
 # 'frame'; and we've seen that it is non-empty
 # as long as we don't read frame.f_locals.