Subprocess writing stdin and reading stdout python 3.4

Question

I am writing a script which would run a Linux command and write a string (up to EOL) to stdin and read a string (until EOL) from stdout. The easiest illustration would be cat - command:

p=subprocess.Popen(['cat', '-'], stdin=subprocess.PIPE, stdout=subprocess.PIPE) stringin="String of text\n" p.stdin.write=(stringin) stringout=p.stout.read() print(stringout)

I aim to open the cat - process once and use it to write a string multiple times to its stdin every time getting a string from its stdout.

I googled quite a bit and a lot of recipes don't work, because the syntax is incompatible through different python versions (I use 3.4). That is my first python script from scratch and I find the python documentation to be quite confusing so far.

monkeywrench · Accepted Answer · 2016-01-22 10:27:48Z

Thank you for your solution Salva. Unfortunately communicate() closes the cat - process. I did not find any solution with subprocess to communicate with the cat - without having to open a new cat - for every call. I found an easy solution with pexpect though:

import pexpect p = pexpect.spawn('cat -') p.setecho(False) def echoback(stringin): p.sendline(stringin) echoback = p.readline() return echoback.decode(); i = 1 while (i < 11): print(echoback("Test no: "+str(i))) i = i + 1

In order to use pexpect Ubuntu users will have to install it through pip. If you wish to install it for python3.x, you will have to install pip3 (python3-pip) first from the Ubuntu repo.

Salva · Accepted Answer · 2016-01-15 15:48:59Z

Well you need to communicate with the process:

from subprocess import Popen, PIPE s = Popen(['cat', '-'], stdin=PIPE, stdout=PIPE, stderr=PIPE) input = b'hello!' # notice the input data are actually bytes and not text output, errs = s.communicate(input)

To use unicode strings, you would need to encode() the input and decode() the output:

from subprocess import Popen, PIPE s = Popen(['cat', '-'], stdin=PIPE, stdout=PIPE, stderr=PIPE) input = 'España' output, errs = s.communicate(input.encode()) output, errs = output.decode(), errs.decode()

Collectives™ on Stack Overflow

Subprocess writing stdin and reading stdout python 3.4

2 Answers 2

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Related