tar_fileobj = io.BytesIO()   
with tarfile.open(fileobj=tar_fileobj, mode="w|") as tar:
    my_content = "abdef".encode('utf-8')
    tf = tarfile.TarInfo("my_file_name")
    tf.size = len(my_content)
    tar.addfile(tf, io.BytesIO(my_content))  
tar_fileobj.seek(0)