install_requires based on python version

This has been discussed here, it would appear the recommend way is to test for the Python version inside your setup.py using sys.version_info;

import sys

if sys.version_info >= (3,2):
    install_requires = ["threadpool >= 1.2.7"]
else:
    install_requires = ["threadpool >= 1.2.3"]

setup(..., install_requires=install_requires)

Use environment markers:

install_requires=[
    'threadpool >= 1.2.7; python_version < "3.2.0"',
]

Setuptools specific usage is detailed in their documentation. The syntax shown above requires setuptools v36.2+ (change log).