def is_existing_up_to_date(destination, latest_version):
    """Returns False if there is no existing install or if the existing install
    is out of date. Otherwise, returns True."""
    version_path = os.path.join(
        destination, 'google_appengine', 'VERSION')

    if not os.path.exists(version_path):
        return False

    with open(version_path, 'r') as f:
        version_line = f.readline()

        match = SDK_RELEASE_RE.match(version_line)

        if not match:
            print('Unable to parse version from:', version_line)
            return False

        version = [int(x) for x in match.groups()]

    return version >= latest_version
Returns False if there is no existing install or if the existing install
    is out of date. Otherwise, returns True.