Following the documentation for setting up Sphinx documentation links between packages, I have added
intersphinx_mapping = {\'python\': (\'http://docs.python.or
It is possible to manually specify which inventory to look. For example, if intersphinx_mapping['sphinx'] = ('http://sphinx-doc.org/', None)
does not work, you can always download the inventory and manually append it to the mapping (e.g. download from http://sphinx-doc.org/objects.inv, save the binary file in your docs and append the path to it in the mapping; this will give something like:
intersphinx_mapping['sphinx'] = ('http://sphinx-doc.org/', ('objects.inv', ), )
To verify if a reference exists within the inventory, you can explore the binary with the sphobjinv python package and check where is the reference you want.
This may not be a solution to your problem but can help to debug some things.