JL> from subprocess import call
 JL> cmd='scp -i id_rsa sample.txt jack@192.168.1.103 /home/jack/pi_data'
 JL> call (cmd.split ())

are you using ssh keys for authentication? 

I've got some python working to transfer data.
here is a command. 
use the subprocess. 

subprocess.call("scp -q %s user@host:/path/file" %(inputfile, s), shell =
True)

you will need to make sure you have keys on the target system basically the
host. 

--- Mystic BBS v1.12 A31 (Windows)