def _prepare_file_payload(filename):
        """
        Prepare `filename` to be sent to the server.

        The "preparation" consists of creating a data structure suitable
        for passing to requests.request().
        """
        if not filename: return None
        absfilename = os.path.abspath(filename)
        if not os.path.exists(absfilename):
            raise H2OValueError("File %s does not exist" % filename, skip_frames=1)
        return {os.path.basename(absfilename): open(absfilename, "rb")}
Prepare `filename` to be sent to the server.

        The "preparation" consists of creating a data structure suitable
        for passing to requests.request().