def __init__(self, url=None):
        """
        Initialise an instance.

        :param url: The URL of the index. If not specified, the URL for PyPI is
                    used.
        """
        self.url = url or DEFAULT_INDEX
        self.read_configuration()
        scheme, netloc, path, params, query, frag = urlparse(self.url)
        if params or query or frag or scheme not in ('http', 'https'):
            raise DistlibException('invalid repository: %s' % self.url)
        self.password_handler = None
        self.ssl_verifier = None
        self.gpg = None
        self.gpg_home = None
        with open(os.devnull, 'w') as sink:
            # Use gpg by default rather than gpg2, as gpg2 insists on
            # prompting for passwords
            for s in ('gpg', 'gpg2'):
                try:
                    rc = subprocess.check_call([s, '--version'], stdout=sink,
                                               stderr=sink)
                    if rc == 0:
                        self.gpg = s
                        break
                except OSError:
                    pass

        Initialise an instance.

        :param url: The URL of the index. If not specified, the URL for PyPI is
                    used.
        
product/gradle-plugin/src/main/python/pip/_vendor/distlib/index.py