import subprocess, time

command = "plink.exe -ssh -l admin -pw admin -C 192.168.1.1"
p = subprocess.Popen(command, stdout=subprocess.PIPE, stdin=subprocess.PIPE)
p.stdin.write('yn')
time.sleep(3)
p.stdin.write('echo "hello world"')
for line in iter(p.stdout.readline, b''):
    print line
p.stdout.close()
p.wait()