pip - setup.py: restrict the allowable version of the python interpreter

Question

I have a Python library. Unfortunately I have not updated it to work with Python 3 yet.

In its setup.py, I added

install_requires=['python<3'],

My intent was to not allow this package to be installed/used under Python 3, because I know it doesn't (yet) work. I don't think this is the right way to do it, because pip then tries to download and install python 2.7.3 (which is already the installed version!).

How should I specify my library dependency on a particular range of Python interpreter versions? Should I add a Programming Language :: Python :: 2 :: Only tag? Will this actually prevent installation under Python 3? What if I also want to restrict the minimum version to Python 2.6?

I'd prefer a solution that works everywhere, but would settle for one that only works in pip (and hopefully doesn't cause easy_install to choke).

Answer 1

As of version 9.0.1 pip will honor a new python_requires string, specifying the Python version required for installation, e.g, for example if one wishes to enforce minimum Python version of 3.3:

setup(
    ...,
    python_requires=">=3.3"
)

See here for more details. See also this answer on SO.