[issue36188] Remove vestiges of Python 2 unbound methods from Python 3

[Martijn Pieters]

New submission from Martijn Pieters <mj at python.org>:

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.

----------
components: Interpreter Core
messages: 337142
nosy: mjpieters
priority: normal
severity: normal
status: open
title: Remove vestiges of Python 2 unbound methods from Python 3
versions: Python 3.6, Python 3.7, Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue36188>
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