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I have been trying to create a python script which opens a exe file, enters an input, then reads an output, and based on the output that was received enter another input.

I've been trying to use Python's subprocess library, but the problem is that the communicate() method can only be used once. so it is impossible to enter 2 inputs unless you enter them both in the communicate() method, which doesn't work in this case. because the second input is based upon the output which is generated after the first input, so you can't enter both inputs at the same time.

Also, I searched for 3rd party libraries for python but I didn't find any good libraries for windows.

Can someone show me a way of performing this action using the subprocess library or suggest me a good library for windows?

always-a-learner
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itai neria
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  • `Popen.communicate()` is just a convenience - you can directly interact with the `.stdin` and `.stdout` attributes (calling `.write()` and `.readline()`, perhaps) to handle more complex situations. – jasonharper Jul 18 '17 at 16:27

1 Answers1

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Consider a simple app that has some basic execution control flow and just echoes its STDIN in reverse to the STDOUT - this can be any executable but we'll stick with Python for simplicity - say, app.py:

#!/usr/bin/env python

import sys

sys.stdout.write("::BEGIN::\n")  # tell our listener that we're listening...
sys.stdout.flush()  # flush the STDOUT buffer
while True:  # a simple event loop
    line = sys.stdin.readline().rstrip()  # read a line from STDIN
    if line:  # ignore empty lines
        if line == "::END::":  # just a convenient way to shut down the app
            sys.stdout.write("::END::\n")  # tell our listener that we're done
            sys.stdout.flush()  # flush the STDOUT buffer
            break  # we're finished here
        sys.stdout.write(line[::-1])  # write the reversed line to STDOUT
        sys.stdout.write("\n")  # add a new line to the STDOUT
        sys.stdout.flush()  # flush the STDOUT buffer

Then if you want to open this app and communicate with it from your Python script all you need to do is control the subprocesses STDOUT and STDIN and you can do this indefinitely, for example:

import subprocess

# start our subprocess, forward its STDOUT and STDIN to the internal buffers
proc = subprocess.Popen(["python", "app.py"], stdout=subprocess.PIPE, stdin=subprocess.PIPE)

# lets define our data to be sent one by one to our app.py, including ::END:: to exit...
items = ["test", "data", "to", "run", "sequentially", "::END::"]

# a convenience function to get the next item and write it to the passed buffer
def send_next_item(buf):
    item = items.pop(0)  # pop the first element from `items`
    print("REQ: {}".format(item))
    buf.write(item)  # write it to the passed buffer
    buf.write("\n")  # write a new line to the passed buffer
    buf.flush()  # flush the passed buffer

while True:  # wait for a prompt by our app
    line = proc.stdout.readline().rstrip()
    if line == "::BEGIN::":
        print("BEGIN!")
        send_next_item(proc.stdin)  # send the first item to the processes' STDIN
    elif line == "::END::":
        print("END!")
        break  # nothing more to do
    elif line:  # ignore empty lines
        print("RES: {}".format(line))
        send_next_item(proc.stdin)  # send the next item to the processes' STDIN

When you run this you'd get an output like:

BEGIN!
REQ: test
RES: tset
REQ: data
RES: atad
REQ: to
RES: ot
REQ: run
RES: nur
REQ: sequentially
RES: yllaitneuqes
REQ: ::END::
END!

Of course, you can do further processing to decide on how to properly respond to the called application's input request, this is just a basic example.

zwer
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