#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""Installs dependencies appropriate for the Python version."""
import subprocess
import sys

subprocess.call("pip", "install --use-mirrors -r requirements.txt")
if sys.version_info[0] >= 3: # Python 3
    # No Python 3-specific dependencies right now
    pass
else:  # Python 2
    subprocess.call("pip", "install --use-mirrors unittest2")

Install different deps for Python 3 vs. Python 2.
Install different deps for Python 3 vs. Python 2.
