setup.py setup_requires implementation, first stab. To install things that are imported by setup.py itself.

setup.py

#!/usr/bin/env python
# Install setup-requires before running setup.py

import sys
sys.path[0:0] = ['setup-requires']

import os, subprocess, pkg_resources

try:
    requirements = [x.strip() for x in open('setup-requires.txt', 'r').readlines()]
except IOError: # file not found?
    requirements = []

to_install = []

for requirement in requirements:
    if not requirement or requirement.strip().startswith('#'):
        continue
    try:
    	pkg_resources.require(requirement)
    except pkg_resources.DistributionNotFound:
        to_install.append(requirement)

if to_install:
    subprocess.call([sys.executable, "-m", "pip", "install", "-t", "setup-requires"] + to_install)

# Now run real setup.py...
exec(compile(open("real-setup.py").read().replace('\\r\\n', '\\n'),
    __file__,
    'exec'))