python - Sending a password over SSH or SCP with subprocess.Popen

Question

I'm trying to run an scp (secure copy) command using subprocess.Popen. The login requires that I send a password:

from subprocess import Popen, PIPE

proc = Popen(['scp', "user@10.0.1.12:/foo/bar/somefile.txt", "."], stdin = PIPE)
proc.stdin.write(b'mypassword')
proc.stdin.flush()

This immediately returns an error:

user@10.0.1.12's password:
Permission denied, please try again.

I'm certain the password is correct. I easily verify it by manually invoking scp on the shell. So why doesn't this work?

Note, there are many similar questions to this, asking about subprocess.Popen and sending a password for automated SSH or FTP login:

How can I set a users password in linux from a python script?
Use subprocess to send a password

The answer(s) to these questions don't work and/or don't apply because I am using Python 3.

Answer 1

The second answer you linked suggests you use Pexpect(which is usually the right way to go about interacting with command line programs that expect input). There is a fork of it which works for python3 which you can use.