py 1.5 release breaks pytest with pip dependency resolver

[uSpike]

Hi,

Since pip doesn't have a great dependency resolver (see pypa/pip#988) it will download the latest version of the dependencies of the first package passed to it. For example,

pip install tox pytest

This will install py>=1.4.17 as depended on by tox, which will happily get the most recent py package at version 1.5. However, we cannot run pytest now since pytest depends on py<1.5

I think you can make the argument that the blame doesn't fall within pytest itself, but I think there's going to be a lot of requirements.txt out there which don't list pytest first, and may run into this issue.

[nicoddemus]

Hi @uSpike,

Thanks for bringing this to attention.

Hmm, the only reason why the <1.5 restriction was put into place was because 1.5 no longer supports py26 and py33. I guess that's a little harsh, perhaps the ideal would be to make the <1.5 restriction valid only for py26 and py33 I guess. This can still cause havoc on those platforms, but I'm sure the affected users will be much fewer.

Alternatively, we might remove the restriction in pytest completely and let py declare python_requires instead.

[nicoddemus]

I went ahead and opened #2927 removing the restriction; as soon as we decide this is the way to go we just push the package to PyPI.

[nicoddemus]

let py declare python_requires instead.

Oh oh, seems it is too late now; publishing a new py-1.5.1 with python_requires won't help because 1.5.0 is already out and it no longer supports py26 and py33. ☹️

[RonnyPfannschmidt]

we can pull the release from pypi if necessary

[RonnyPfannschmidt]

after all it breaks the world

[nicoddemus]

3.2.5 has been published with the restriction removed, thanks @uSpike again for the quick report.

[uSpike]

Thanks for the quick response @nicoddemus and @RonnyPfannschmidt !

Hopefully pip can get a good dependency resolver in place soon :)

[merwok]

FIW pip-compile from the https://github.com/jazzband/pip-tools project can handle this kind of situtations.