Serhiy posted a patch at http://bugs.python.org/issue29537 that addresses the original problem from http://bugs.python.org/issue27286 in a different way: it simply omits the function name in cases where the stack reference is ambiguous.

So what I think we should do for 3.5.4 is implement the one-off patch that allows the remainder of the 3.5.x series to accept both the original 3.5.0 magic number and the 3.5.3+ magic number, in combination with Serhiy's change to the eval loop to render any malformed legacy bytecode harmless.

The 2.7, 3.6 and master branches can then just get the test case that locks the bytecode to a particular value in any given branch that has reached release candidate status.