How can I put an intersphinx link to an arbitrary method in the standard library documentation?

The :py:meth: should be :py:func:. Basically, any valid domain can be used.

Have you read the documentation for intersphinx?

Edit

Got it to work using this:

***
TRY
***

My try
======

sin
:py:func:`math.cos`

pop
:py:meth:`dict.pop`

dict
:py:meth:`dict.items`

zipfile
:py:class:`zipfile.ZipFile`

Read about the constructs here crossreference

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