Can you set conditional dependencies for Python 2 and 3 in setuptools?

Question

When releasing a Python egg with support for both Python 2 and 3, can you specify dependencies that change depending on which version you\'re using? For example, if you use

Answer 1

For something mostly related but not exactly to the point see my answer https://stackoverflow.com/a/25078063/302521 and this script: https://gist.github.com/pombredanne/72130ee6f202e89c13bb

Answer 2

Bogdan's comment helped point me on my way. I thought I'd post what I did in case anyone else has my problem.

For the example in the question, I did exactly what Bogdan suggested:

setup.py

import sys

if sys.version_info[0] == 2:
    dnspython = "dnspython"
elif sys.version_info[0] == 3:
    dnspython = "dnspython3"

setup(
    ... <snip> ...
    install_requires=[
        "%s >= 1.10.0" % dnspython,
    ]
)

However, this still has the issue of pip-style dependencies for Travis and tox (I'm not sure why, given Bogdan's second comment). To work around this problem, I created two extra requirements files, as shown below:

requirements-py2.txt

dnspython>=1.10.0

requirements-py3.txt

dnspython3>=1.10.0

Then for Travis, I made use of some environment variables that I gleaned from the tornado .travis.yml:

.travis.yml

install:
  - if [[ $TRAVIS_PYTHON_VERSION == 2* ]]; then pip install -r requirements-py2.txt --use-mirrors; fi
  - if [[ $TRAVIS_PYTHON_VERSION == 3* ]]; then pip install -r requirements-py3.txt --use-mirrors; fi

Lastly, for tox, I had to use a rather hackish method of using these multiple requirements files.

tox.ini

[testenv:py27]
deps = -rrequirements-py2.txt

[testenv:py33]
deps = -rrequirements-py3.txt

Answer 3

The setup.py portion of the answer by @Harold did not work for me: pip install distribution.whl still installs the dependency that the if code says it shouldn't. I will further update this answer in a few days when I have this issue resolved.

Here are some links that may provide additional ways to deal with this ():

• Wheel docs section explaining conditional dependencies: not completely clear but gives a hint of what to do
• Example on github
• Blog post