[Distutils] PEP439 and backward compat / easy_install / distlib

[Ronald Oussoren]

On 26 Mar, 2013, at 12:06, Daniel Holth <dholth at gmail.com> wrote:

> 
> On Mar 26, 2013 5:28 AM, "Ronald Oussoren" <ronaldoussoren at mac.com> wrote:
> >
> >
> > On 25 Mar, 2013, at 19:16, PJ Eby <pje at telecommunity.com> wrote:
> > >
> > >
> > > Also, as far as detecting the need for setuptools, I think that can be
> > > done just by noticing whether the PKG-INFO included in an sdist is
> > > metadata 2.0 or not.  If it is, then setuptools should be explicitly
> > > declared as a build-time dependency, otherwise it's not needed.  If
> > > it's an older metadata version, then you probably need setuptools.
> >
> > Is it even necessary to automaticly install setuptools? Setuptools-using package are supposed to use  ez_setup.py, or distribute_setup.py for distribute, to ensure that the setuptools package is available during setup.  Although I must admit that I have no idea how many packages still do this instead of assuming that users will have installed setuptools anyway.
> >
> > Ronald
> >
> 
> We really really really want to get rid of ez_setup. It is considered by many to be the example of something that should not happen as a side effect of running a build script.

That can't be helped with the current tool versions, distutils in current release of python doesn't support setup-requires and hence the only way to use setuptools is by using ez_setup.py.  Ez_setup.py will still have to be present for python 2.7 users that want to use "python setup.py ...", and hence can be assumed to be present for now.  I'm all for adding support for metadata 2.0 to the stdlib for Python 3.4, that way ez_setup.py can be phased out in the long run.

> 
> When packages no longer have to install themselves, they can just mention setup-requires and the installer grabs the necessary setuptools.
> 
That can only be done for sdists with 2.0 metadata, sdists for older versions don't have a setup-requires in their metadata.  This is not just for installing, if you want to use setuptools in your setup.py you'll have to make sure it is installed in your setup.py, and with the current version of the packaging tools this means you have to use something like ez_setup.py or tell users to install setuptools themselves.

And with some luck a large subset of packages will ship wheels in the future, that way the installer doesn't even have to look at sdists.

Ronald