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Currently, calling doctest.DocTestSuite() raises a ValueError if the module passed to it has no docstrings. This was the subject of issue 14649.
This issue is to discuss and possibly change DocTestSuite's behavior not to raise an exception in that situation.
In the discussion for issue 14649 (in particular with R. David Murray), it was acknowledged that the current behavior probably isn't correct or desirable. However, treating the behavior as a bug and fixing it in maintenance branches would have been too big of a change.
Thus, if this change is made, it could be slated for the next feature release.

I'm attaching a patch that changes DocTestSuite's default behaviour as suggested.

Hmm. This patch still raises the "has no docstrings" ValueError if "not tests" is True. And because the patch changes the default DocTestFinder, it's possible that the patch changes behavior in non-error use cases.
Why not just return an empty TestSuite if not tests is True? IIRC, this was the conclusion of the issue 14649 discussion.

I've attached a patch that uses the original default DocTestFinder and does not raise an exception when there are no tests.

This looks good, however we also need a documentation change indicating the new behavior, including a '.. versionchanged:: 3.5' tag, and an entry in whatsnew/3.5 in the 'other changes' section.

Added docs to patch

New changeset 57fb5441a4aa by R David Murray in branch 'default':
#15916: if there are no docstrings, make empty suite, not an error.
http://hg.python.org/cpython/rev/57fb5441a4aa 

Thanks, Glenn.