def _pypi_head_package(dependency):
    """Hit pypi with a http HEAD to check if pkg_name exists."""
    if dependency.specs:
        _, version = dependency.specs[0]
        url = BASE_PYPI_URL_WITH_VERSION.format(name=dependency.project_name, version=version)
    else:
        url = BASE_PYPI_URL.format(name=dependency.project_name)
    logger.debug("Doing HEAD requests against %s", url)
    req = request.Request(url, method='HEAD')
    try:
        response = request.urlopen(req)
    except HTTPError as http_error:
        if http_error.code == HTTP_STATUS_NOT_FOUND:
            return False
        else:
            raise
    if response.status == HTTP_STATUS_OK:
        logger.debug("%r exists in PyPI.", dependency)
        return True
    else:
        # Maybe we are getting somethink like a redirect. In this case we are only
        # warning to the user and trying to install the dependency.
        # In the worst scenery fades will fail to install it.
        logger.warning("Got a (unexpected) HTTP_STATUS=%r and reason=%r checking if %r exists",
                       response.status, response.reason, dependency)
        return True
Hit pypi with a http HEAD to check if pkg_name exists.