import pip
from subprocess import check_call
import sys

project_names = {dist.project_name for dist in pip.get_installed_distributions()}

# The scipy and numpy from PyPI aren't compatible on Windows (adjust this list as needed)
project_names -= {"scipy", "numpy"}

# Run this script against each of your Python distributions as desired (even 2.7)
check_call(
    '"%s" -m pip install --upgrade %s' % (sys.executable, " ".join(project_names)),
    shell=True)