class BadStr(str):
    _armed = False
    def __eq__(self, other):
        if BadStr._armed and isinstance(other, str) and str.__eq__(self, other):
            raise RuntimeError("Poison!")
        return str.__eq__(self, other)
    def __hash__(self): return str.__hash__(self)

c1 = compile("pass", "test", "exec")
c2 = c1.replace(co_name=BadStr("poison"))
c3 = compile("pass", "poison", "exec")
BadStr._armed = True
c2 == c3  # assertion: !_PyErr_Occurred(tstate)