pypi - "no source distribution" for some packages

[Mayuresh <mayuresh%acm.org@localhost>]

For a routine upgrade of some wip packages, in this case wip/py-mozrunner,
I went to look for the latest version here [1].

Came across this comment on the page:

 "No source distribution files available for this release. See tutorial on
 generating distribution archives."

I'd have thought it's a one off case with a package. But further the
tutorial page [2] says this:

    "Newer pip versions preferentially install built distributions, but
    will fall back to source distributions if needed."

That's a bit worrying.

If this is a trend, how should the packaging systems like pkgsrc deal with
it?

Larger question apart, any suggestions on how to go about upgrading
mozrunner to the latest version?

-- 
Mayuresh

[1] https://pypi.org/project/mozrunner/#files
[2] https://packaging.python.org/en/latest/tutorials/packaging-projects/#generating-distribution-archives