<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def upload_file_mp(self, container, src_file_path, dst_name=None, content_type=None):
 """Upload a file using multi-part encoding."""

        if not os.path.exists(src_file_path):
            raise RuntimeError('file not found: ' + src_file_path)
        if not dst_name:
            dst_name = os.path.basename(src_file_path)
        if not content_type:
            content_type = "application/octet.stream"
        url = self.make_url(container, None, None)
        headers = self._base_headers
        with open(src_file_path, 'rb') as up_file:
            files = {'file': (dst_name, up_file, content_type)}
            try:
                rsp = requests.post(url, headers=headers, files=files,
                                    timeout=self._timeout)
            except requests.exceptions.ConnectionError as e:
                RestHttp._raise_conn_error(e)

        return self._handle_response(rsp)