How to make Python's subprocess() interact with input()?

The problem is that readline reads a stream until it finds a newline, and that input("Which action to use? ") does not print one.

One simple workaround would be to write

...
reply = input("Which action to use? \n")
...

If you do not want (or cannot) to change anything in test menu, you will have to implement a read with timeout, or read one char at a time until you find either a new line or a ?.

For example this should work:

...
def terminated_read(fd, terminators):
 buf = []
 while True:
 r = fd.read(1).decode()
 buf += r
 if r in terminators:
 break
 return ''.join(buf)
process = subprocess.Popen(cmd,
 shell=False,
 bufsize=0,
 stdin=subprocess.PIPE,
 stdout=subprocess.PIPE,
 stderr=subprocess.PIPE)
for i in range(8):
 output = terminated_read(process.stdout, "\n?")
 print(output.strip())
...

Passing the answer to subprocess is simple. The hard part is to guess when to answer. Here, you know that you can answer as soon as an input ends in ?. I changed your test_menu.py to be able to confirm that it correctly get the command to:

#!/usr/bin/env python3
import sys
action_text = """
5. Perform addition
6. Perform subtraction
Q. Quit
"""
def get_action():
 print(action_text)
 reply = input("Which action to use? ")
 print("Was asked ", reply) # display what was asked
 if reply == '5':
 print("subtract...")
if __name__ == "__main__":
 get_action()

The wrapper test1.py is then simply:

import subprocess
cmd = ["/usr/bin/python3","./test_menu.py"]
def terminated_read(fd, terminators):
 buf = []
 while True:
 r = fd.read(1).decode()
 # print(r)
 buf.append(r)
 if r in terminators:
 break
 return "".join(buf)
process = subprocess.Popen(cmd,
 shell=False,
 bufsize=0,
 stdin=subprocess.PIPE,
 stdout=subprocess.PIPE,
 stderr=subprocess.PIPE)
while True:
 output = terminated_read(process.stdout, "\n?")
 print(output.strip())
 if output[-1] == '?':
 break
process.stdin.write(('%s\n' % "5").encode())
cr = process.wait()
end = process.stdout.read().decode()
print("Child result >" + end + "<")
print("Child code" + str(cr))

Started with either Python 3.4 or Python 2.7 the output is as expected:

5. Perform addition
6. Perform subtraction
Q. Quit
Which action to use?
Child result > Was asked 5
subtract...
<
Child code0

The following should work (the main difference is that this stops reading stdout when it encounters the end of the menu):

test1.py:

#!/usr/bin/env python
import subprocess
cmd = ['./test_menu.py']
p = subprocess.Popen(cmd, shell=False, bufsize=0
 stdin=subprocess.PIPE, 
 stdout=subprocess.PIPE)
menu = ''
while True:
 output = p.stdout.read(1)
 if output:
 menu += output
 else:
 break
 if menu.endswith('#: '):
 break
print(p.communicate(raw_input(menu))[0])

test_menu.py:

#!/usr/bin/env python
import sys
action_text = '''
5. Perform addition
6. Perform subtraction
Q. Quit
#: '''
sys.stdout.write(action_text); sys.stdout.flush()
inp = sys.stdin.read()
print(inp)

Usage:

[ 12:52 me@yourbase ~/test ]$ ./test1.py 
5. Perform addition
6. Perform subtraction
Q. Quit
#: 5
5
[ 12:52 me@yourbase ~/test ]$ ./test1.py 
5. Perform addition
6. Perform subtraction
Q. Quit
#: 12345
12345

Not sure what you are planning after but the following will take input and you can do whatever you want with it in get_action:

action_text = """5. Perform addition
6. Perform subtraction
Q. Quit"""
def get_action():
 print(action_text)
 inp = input("Which action to use?\n")
 print(inp)
 print("Now do whatever")
if __name__ == "__main__":
 get_action()
import subprocess
cmd = ["/usr/bin/python3","./test_menu.py"]
process = subprocess.Popen(cmd,
 shell=False,
 bufsize=0,
 stdin=subprocess.PIPE,
 stdout=subprocess.PIPE,
 stderr=subprocess.PIPE)
for line in iter(process.stdout.readline, ""):
 print(line)
 if line.rstrip() == "Which action to use?":
 r = raw_input()
 process.stdin.write(r+"\n")

A sample run:

5. Perform addition
6. Perform subtraction
Q. Quit
Which action to use?
6
6
Now do whatever

Adding a couple of functions:

def add():
 return 4+ 6
def sub():
 return 4 - 6
def get_action():
 print(action_text)
 inp = input("Which action to use?\n")
 if inp == "5":
 print(add())
 elif inp == "6":
 print(sub())
 else:
 print("Goodbye")
if __name__ == "__main__":
 get_action()

Outputs:

5. Perform addition
6. Perform subtraction
Q. Quit
Which action to use?
6
-2

Add:

5. Perform addition
6. Perform subtraction
Q. Quit
Which action to use?
5
10

Anything else:

5. Perform addition
6. Perform subtraction
Q. Quit
Which action to use?
q
Goodbye

If you want to write without taking any input from a user, forget r and just write to stdin:

for line in iter(process.stdout.readline, ""):
 print(line)
 if line.rstrip() == "Which action to use?":
 process.stdin.write("5\n")

Ouput:

5. Perform addition
6. Perform subtraction
Q. Quit
Which action to use?
10

If you're using a linux system it's as easy as running the program as follows:

printf "5" | python3 "tests1.py"

If you have a python script with multiple questions, just answer each one with a "\n" character in between. For example:

printf "1\n2\n3\n4\n5" | (The command to run your script)

Will answer the first question with "1", the second with "2" and so forth.

This solution works for any interactive script on prompt written in any language. For more information on how to use bash to interact with scripts, there's this post I learned from:

https://www.baeldung.com/linux/bash-interactive-prompts

(This is my first answer in Stack Overflow so the format might be a little weird. Anyways, hope I can help anyone going through this problem as I was.)

• python
• python-3.x
• pipe
• subprocess
• popen