If you really want something like this, you can today write:

    >>> def wibble(fn):
    ...     return ', '.join(fn())

    >>> @wibble
    ... def aaaa():
    ...     return 'APPLES'

    >>> aaaa
    'A, P, P, L, E, S'

This allows you to use a decorator, if that's really what you want to do.

The original post asked for
to be equivalent to
     fruit = wibble(fruit)

If there are sufficient examples where this is useful, I say go for it. But only after first trying to get my fruit in some other way.

Real world examples where it would be useful are generally worth much more than invented examples.

I hope this helps, even if it disappoints.