[Python-ideas] Add __parent__ to all classes, functions, and modules

[Neil Girdhar]

Many classes, functions, and modules are defined within the context of 
another class, function, or module thereby forming a mathematical forest of 
declarations.  It is possible to walk the descendants using __dict__ (for 
classes and modules), but not the ancestors.  I propose adding __parent__ 
that would be filled at the same time that __qualname__ is filled in.  One 
concrete use case for __parent__ is allowing a method decorator to call 
super, which is currently impossible because the class in which the method 
has been defined is not available to the decorator.  This way, one could 
write:

def ensure_finished(iterator):
    try:
        next(iterator)
    except StopIteration:
        return
    else:
        raise RuntimeError

def derived_generator(method):
    def new_method(self, *args, **kwargs):
        x = method(self, *args, **kwargs)
        y = getattr(super(method.__parent__, self), method.__name__)\
            (*args, **kwargs)

        for a, b in zip(x, y):
            assert a is None and b is None
            yield

        ensure_finished(x)
        ensure_finished(y)

This is currently impossible to implement without restating the class name 
every time the decorator is used as far as I know.

Best,

Neil
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