Sphinx: How to link to terms in a glossary of a different project

Question

I do understand how to create a glossary in Sphinx RST, and how to link to its terms:

.. glossary::

   term1
      description of term1

Linking to :term:`term1` is easy.

My question is, how can I link to terms in the glossary of a different Sphinx project, for which I have an intersphinx definition?

For example, I have an intersphinx definition for the Sphinx documentation of Python 2:

intersphinx_mapping = {
  'py': ('https://docs.python.org/2/', None),
}

But I was not successful in specifying a link to one of its glossary terms, using any of these constructs in the RST source:

:ref:`py:iterable`
:ref:`py:glossary.iterable`
:term:`py:iterable`
:term:`py:glossary.iterable`

Is that possible, and if so how does the definition of the glossary need to look like and how the reference to a glossary term?