At the problematic breakpoint mentioned in msg255630, copy_reg is nearly empty.
(Pdb) sys.modules['copy_reg']
<module 'copy_reg' from '/build/python2.7-96oGYh/python2.7-2.7.11~rc1/Lib/copy_reg.pyc'>
(Pdb) dir(sys.modules['copy_reg'])
['__builtins__', '__doc__', '__file__', '__name__', '__package__']
(Pdb) sys.modules['copy_reg'].__file__
'/build/python2.7-96oGYh/python2.7-2.7.11~rc1/Lib/copy_reg.pyc'
(Pdb) sys.modules['copy_reg'].__doc__
(Pdb) sys.modules['copy_reg'].__name__
'copy_reg'
(Pdb) sys.modules['copy_reg'].__package__