ssh_client = paramiko.SSHClient()
ssh_client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh_client.load_system_host_keys()
ssh_client.connect('server', username='username', password='cfwc')

stdin, stdout, stderr = ssh_client.exec_command ('(cat /path to/a.txt |  cd /path to files ; ./script > b.txt )')

stdin, stdout, stderr = ssh_client.exec_command ('(cat a.txt |  cd /path to files/script > b.txt )')