Question

Suppose I have a simple C++ program that takes in inputs and outputs some string. Like this (actual program is much more complicated but still text based):

$ ./game
$ what kind of game? type r for regular, s for special.
$ r
$ choose a number from 1 - 10
$ 1
$ no try again
$ 2
$ no try again
$ 5
$ yes you WIN!

I haven’t used Python before, but is it possible to write a python script to run this program, feeds it input, and outputs the results to standard output? I have ask the question here about running it using C++ but it seems much too complicated. It would be awesome it you could direct me to some code examples. Any help would be appreciated.

Answer 1

Use pexpect.

Normal stdin/stdout piping usually doesn’t work, because the standard library facilities in the parent and child processes tend to buffer I/O more aggressively when a file descriptor isn’t a TTY (via the isatty call). Obviously, you can fix this in the parent, since you own that code; just call flush at appropriate points. But often the child process is running some preexisting code that you don’t own. The pexpect module feeds the child process a pseudo-tty, which tricks the child into thinking it’s talking to a console. This is the same trick that GUI terminals like xterm and rxvt use.