How to ensure that README.rst is valid?

Preamble

I had a readme which would not render on PyPi, other than the first element on the page (an image). I ran the file against multiple validators, and tested it against other renders. It worked perfectly fine everywhere else! So, after a long, nasty fight with it, and numerous version bumps so I could test a PyPi revision, I tried reducing the file to a bare minimum, from which I'd build it back up. It turned out that the first line was always processed, and then nothing else was...

Solution

Discovering this clue regarding the first line, I then had an epiphany... All I had to do was change the line endings in the file! I was editing the file in Windows, with Windows line endings being tacked on implicitly. I changed that to Unix style and (poof!) PyPi fully rendered the doc!

Rant...

I've encountered such things in the past, but I took it for granted that PyPi would handle cross platform issues like this. I mean one of the key features of Python is being cross platform! Am I the first person working in Windows to encounter this?! I don't appreciate the hours of time this wasted.

Update

As of Sep 21, 2018, the Python Packaging Authority recommends an alternative command twine check. To install twine:

pip install twine
twine check dist/*

Note that twine requires readme_renderer. You could still use readme_renderer, and you only need to install twine if you want its other features, which is a good idea anyway if you are releasing to PyPI.

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From the official Python packaging docs, Uploading your Project to PyPI:

Tip: The reStructuredText parser used on PyPI is not Sphinx! Furthermore, to ensure safety of all users, certain kinds of URLs and directives are forbidden or stripped out (e.g., the .. raw:: directive). Before trying to upload your distribution, you should check to see if your brief / long descriptions provided in setup.py are valid. You can do this by following the instructions for the pypa/readme_renderer tool.

And from that tool's README.rst:

To check your long description's locally simply install the readme_renderer library using:

$ pip install readme_renderer
$ python setup.py check -r -s

You could try if rstcheck catches the type of error in your readme. If it does, run it after pytest in your script section. (and add it in your requirements ofc).