Automatically find/download setuptools and make it available on sys.path

    `version` should be a valid setuptools version number that is available
    as an egg for download under the `download_base` URL (which should end with
    a '/').  `to_dir` is the directory where setuptools will be downloaded, if
    it is not already available.  If `download_delay` is specified, it should
    be the number of seconds that will be paused before initiating a download,
    should one be required.  If an older version of setuptools is installed,
    this routine will print a message to ``sys.stderr`` and raise SystemExit in
    an attempt to abort the calling script.

def use_setuptools(
    version=DEFAULT_VERSION, download_base=DEFAULT_URL, to_dir=os.curdir,
    download_delay=15
):
    """Automatically find/download setuptools and make it available on sys.path

    `version` should be a valid setuptools version number that is available
    as an egg for download under the `download_base` URL (which should end with
    a '/').  `to_dir` is the directory where setuptools will be downloaded, if
    it is not already available.  If `download_delay` is specified, it should
    be the number of seconds that will be paused before initiating a download,
    should one be required.  If an older version of setuptools is installed,
    this routine will print a message to ``sys.stderr`` and raise SystemExit in
    an attempt to abort the calling script.
    """
    was_imported = 'pkg_resources' in sys.modules or 'setuptools' in sys.modules
    def do_download():
        egg = download_setuptools(version, download_base, to_dir, download_delay)
        sys.path.insert(0, egg)
        import setuptools; setuptools.bootstrap_install_from = egg
    try:
        import pkg_resources
    except ImportError:
        return do_download()       
    try:
        pkg_resources.require("setuptools>="+version); return
    except pkg_resources.VersionConflict, e:
        if was_imported:
            print >>sys.stderr, (
            "The required version of setuptools (>=%s) is not available, and\n"
            "can't be installed while this script is running. Please install\n"
            " a more recent version first, using 'easy_install -U setuptools'."
            "\n\n(Currently using %r)"
            ) % (version, e.args[0])
            sys.exit(2)
    except pkg_resources.DistributionNotFound:
        pass

    del pkg_resources, sys.modules['pkg_resources']    # reload ok
    return do_download()