Setuptools pulls down incompatible version of package with develop

Context: IPython just released 6.0rc1 on to PyPI, which is only compatible with 3.3+. pip install ipython on python 2.7 pulls down IPython 5.3.0 as you’d expect when invoked as pip install ipython. However, setuptools instead pulls down IPython 6.0 leading to an installation error.

Minimally reproducible example:

# setup.py
from setuptools import setup

setup(
    name='example',
    install_requires=['ipython'],
)

Outputs:

(env) $ python -c 'import pkg_resources; print pkg_resources.get_distribution("setuptools")'
setuptools 34.4.1
(env) $ python setup.py develop
running develop
running egg_info
writing requirements to example.egg-info/requires.txt
writing example.egg-info/PKG-INFO
writing top-level names to example.egg-info/top_level.txt
writing dependency_links to example.egg-info/dependency_links.txt
reading manifest file 'example.egg-info/SOURCES.txt'
writing manifest file 'example.egg-info/SOURCES.txt'
running build_ext
Creating /Users/jtratner/env/lib/python2.7/site-packages/example.egg-link (link to .)
example 0.0.0 is already the active version in easy-install.pth

Installed /Users/jtratner
Processing dependencies for example==0.0.0
Searching for ipython
Reading https://pypi.python.org/simple/ipython/
Downloading https://pypi.python.org/packages/76/46/c505c48d264715136edde1a1960f9158133e34c03bbfe4c955dbc5948ce4/ipython-6.0.0rc1.tar.gz#md5=e57acb5fabd9f18b739de35a1f00eac5
Best match: ipython 6.0.0rc1
Processing ipython-6.0.0rc1.tar.gz
Writing /var/folders/h2/64h07zpd7576xz6wcq8jdzrw0000gp/T/easy_install-BGbWO9/ipython-6.0.0rc1/setup.cfg
Running ipython-6.0.0rc1/setup.py -q bdist_egg --dist-dir /var/folders/h2/64h07zpd7576xz6wcq8jdzrw0000gp/T/easy_install-BGbWO9/ipython-6.0.0rc1/egg-dist-tmp-zb3BA7

IPython 6.0+ does not support Python 2.6, 2.7, 3.0, 3.1, or 3.2.
When using Python 2.7, please install IPython 5.x LTS Long Term Support version.
Beginning with IPython 6.0, Python 3.3 and above is required.

See IPython `README.rst` file for more information:

    https://github.com/ipython/ipython/blob/master/README.rst

Python sys.version_info(major=2, minor=7, micro=9, releaselevel='final', serial=0) detected.


error: Setup script exited with 1

and on the same system pip does the “right” thing

(env) $ pip install --no-cache-dir -i https://pypi.python.org/simple ipython
# snip...
Successfully installed appnope-0.1.0 backports.shutil-get-terminal-size-1.0.0 decorator-4.0.11 enum34-1.1.6 ipython-5.3.0 ipython-genutils-0.2.0 pathlib2-2.2.1 pexpect-4.2.1 pickleshare-0.7.4 prompt-toolkit-1.0.14 ptyprocess-0.5.1 pygments-2.2.0 scandir-1.5 simplegeneric-0.8.1 traitlets-4.3.2 wcwidth-0.1.7
(env) $ pip uninstall ipython

I’ve tested and this happens on OSX and a centos6 box I have access to.

[Carreau]

It seem your pip is out of date, as pip 9.0.1 seem to not behave as in your screenshot.

MacBook-Pro-4:~ bussonniermatthias$ python2 -m pip --version
pip 9.0.1 from /usr/local/lib/python2.7/site-packages (python 2.7)
MacBook-Pro-4:~ bussonniermatthias$ python2 -m pip install ipython --pre --upgrade
Collecting ipython
  Using cached ipython-5.3.0-py2-none-any.whl

So pip does the right thing.

[tvalentyn]

I observe the same issue with setuptools-41.0.1 on Windows (but not on Linux). Usecase: a project depends on numpy>=1.13.0. On a Windows machine with Python 2.7 and pip==19.1.1, setuptools for test command attempts to pull an incompatible package numpy==1.17.0rc1, which requires Python 3.5. pip install picks up correct version. I assume this issue is still considered WAI.