[Numpy-discussion] Proposal: stop supporting 'setup.py install'; start requiring 'pip install .' instead

[Charles R Harris]

On Mon, Oct 26, 2015 at 10:31 PM, Nathaniel Smith <njs at pobox.com> wrote:

> Hi all,
>
> Apparently it is not well known that if you have a Python project
> source tree (e.g., a numpy checkout), then the correct way to install
> it is NOT to type
>
>   python setup.py install   # bad and broken!
>
> but rather to type
>
>   pip install .
>
> (I.e., pip install isn't just for packages on pypi -- you can also
> pass it the path to an arbitrary source directory or the URL of a
> source tarball and it will do its thing. In this case "install ."
> means "install the project in the current directory".)
>
> These don't quite have identical results -- the main difference is
> that the latter makes sure that proper metadata gets installed so that
> later on it will be possible to upgrade or uninstall correctly. If you
> call setup.py directly, and then later you try to upgrade your
> package, then it's entirely possible to end up with a mixture of old
> and new versions of the package installed in your PYTHONPATH. (One
> common effect is in numpy's case is that we get people sending us
> mysterious bug reports about failing tests in files don't even exist
> (!) -- because nose is finding tests in files from one version of
> numpy and running them against a different version of numpy.)
>
> But this isn't the only issue -- using pip also avoids a bunch of
> weird corner cases in distutils/setuptools. E.g., if setup.py uses
> plain distutils, then it turns out this will mangle numpy version
> numbers in ways that cause weird horribleness -- see [1] for a bug
> report of the form "matplotlib doesn't build anymore" which turned out
> to be because of using 'setup.py install' to install numpy. OTOH if
> setup.py uses setuptools then you get different weirdnesses, like you
> can easily end up with multiple versions of the same library installed
> simultaneously.
>
> And finally, an advantage of getting used to using 'pip install .' now
> is that you'll be prepared for the glorious future when we kill
> distutils and get rid of setup.py entirely in favor of something less
> terrible [2].
>
> So a proposal that came out of the discussion in [1] is that we modify
> numpy's setup.py now so that if you try running
>
>     python setup.py install
>
> you get
>
>     Error: Calling 'setup.py install' directly is NOT SUPPORTED!
>     Instead, do:
>
>         pip install .
>
>     Alternatively, if you want to proceed at your own risk, you
>     can try 'setup.py install --force-raw-setup.py'
>     For more information see http://...
>
> (Other setup.py commands would continue to work as normal.)
>
> I believe that this would also break both 'easy_install numpy', and
> attempts to install numpy via the setup_requires= argument to
> setuptools.setup (because setup_requires= implicitly calls
> easy_install). install_requires= would *not* be affected, and
> setup_requires= would still be fine in cases where numpy was already
> installed.
>
> This would hopefully cut down on the amount of time everyone spends
> trying to track down these stupid weird bugs, but it will also require
> some adjustment in people's workflows, so... objections? concerns?
>

I gave it a shot the other day. Pip keeps a record of the path to the repo
and in order to cleanup I needed to search out the file and delete the repo
path. There is probably a better way to do that, but it didn't strike me as
less troublesome than ` python setup.py install --local`.

Chuck
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