Error compressing tar file

[Mike]

Hello,
I have the script that make a backup file (this process is ok), but now i wish compress the file on tar file format. But i have problem syntax in the line of the tar function. 

The error is 

[root at master ~]# python bkp_db.py 
  File "bkp_db.py", line 19
    tar = tarfile.open(dumpfile)+'.tar.gz','w:gz')
                                                 ^

Note: The 'dumpfile' is the variable for my dump generate with format db_02-27-14

......
tar = tarfile.open(dumpfile)+'.tar.gz','w:gz')
tar.add(os.path.join(dumpfile), arcname=dumpfile)
tar.close()
........

Wath is the correct sintax?


Thanks.