The implementation of method_hash, method_call and method_descr_get all still contain assumptions that __self__ can be set to None, a holdover from Python 2 where methods could be *unbound*.

These vestiges can safely be removed, because method_new() and PyMethod_New() both ensure that self is always non-null.

In addition, the datamodel description of methods includes this section:

      When a user-defined method object is created by retrieving another method
      object from a class or instance, the behaviour is the same as for a
      function object, except that the :attr:`__func__` attribute of the new
      instance is not the original method object but its :attr:`__func__`
      attribute.

which also only applies to Python 2 unbound methods. Python 3 bound methods never change what they are bound to, let alone produce a new method object from __get__ that has to be careful about what __func__ is set to.

I'm submitting a PR that removes these vestiges, no need to maintain code that never runs.

New changeset b727239575894b060db37792e86aab818c00817a by Benjamin Peterson (Martijn Pieters) in branch 'master':
closes bpo-36188: Clean up 'unbound' method left-overs. (GH-12169)
https://github.com/python/cpython/commit/b727239575894b060db37792e86aab818c00817a