Use subprocess to send a password

Perhaps you should use an expect-like library instead?

For instance Pexpect (example). There are other, similar python libraries as well.

Use Paramiko for SFTP. For anything else, this works:

import subprocess

args = ['command-that-requires-password', '-user', 'me']

proc = subprocess.Popen(args, 
                        stdin=subprocess.PIPE, 
                        stdout=subprocess.PIPE, 
                        stderr=subprocess.PIPE)

proc.stdin.write('mypassword\n')
proc.stdin.flush()

stdout, stderr = proc.communicate()
print stdout
print stderr

from subprocess import Popen, PIPE

proc = Popen(['sftp','user@server', 'stop'], stdin=PIPE)
proc.communicate(input='password')

Try with input=‘password’ in communicate, that worked for me.

Try

proc.stdin.write('yourPassword\n')
proc.stdin.flush()

That should work.

What you describe sounds like stdin=None where the child process inherits the stdin of the parent (your Python program).