Using Python, I want to execute an external program, interact with it by providing text to its standard input, and then print the result. As an example, I created the following external program, called test.py: print('Test Program') print('1 First option, 2 Second Option') choice = input() if choice == '1': second_param = input('Insert second param: ') result = choice + ' ' + second_param print(result) If I run this program directly, it works as expected. If I provide the input 1 and then 2, the output is 1 2. I want to run this program from another script and interact with it to print the same result. After reading the documentation for subprocess, I ended up with the following: EXTERNAL_PROG = 'test.py' p = Popen(['py', EXTERNAL_PROG], stdout=PIPE, stdin=PIPE, shell=True) print(p.stdout.readline().decode('utf-8')) print(p.stdout.readline().decode('utf-8')) p.stdin.write(b'1\n') p.stdin.write(b'2\n') print(p.stdout.readline().decode('utf-8')) However, when I run the code, the program freezes after printing 1 First option, 2 Second Option, and I need to restart my shell. This is probably caused by the fact that subprocess.stdout.readline() expects to find a newline character, and the prompt for the second param doesn’t contain one. I found two related questions, but I still couldn’t get it to work. Here, the answer recommends using the pexpect module. I tried to adapt the code to my situation, but it didn’t work. Here, the suggestion is to use -u, but adding it didn’t change anything. I know that a solution can be found by modifying test.py, but this is not possible in my case since I need to use another external program. This is just a minimal example based on it. Continue reading...
