Run Python3 From C

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Written by:
Stephen Andersen
Group 8
Winter 2016
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Introduction

This tutorial or 'app note' will demonstrate how to run python3 from C

This tutorial expects you to understand basic C and Python3.

C Side

SETUP FOR SIGNAL HANDLING

// Have a bool to ensure that if the signal activates, C will notice (Python can be FAST)
bool sig_flag = false;
...
// Init signal handler for first use
sig_handler(0);

SIGNAL HANDLER

void sig_handler(int sig) {
// We have resumed.
// Re-init signal handler
signal(SIGCONT, sig_handler);
sig_flag = true;
return;
}

SOMEWHERE ELSE IN CODE

// Here we write the command to start python into a string
sprintf(buffer, "python3 GA_Code/main.py -p %d", getpid());
// The passing of the pid is important only if you pause for pythons result (via pipelining)

// This runs the string in bash system(buffer);

// WAIT FOR OUTPUT (A SIGNAL FROM PYTHON'S KILL())
// If sig_flag is already true, python finished really fast; no need for pause()
if (!sig_flag)
// Pause() will make C stop executing until killed
pause();
// Reset sig_flag sig_flag = false;

Python Side

SIGNAL HANDLING

def alert_parent_program(pid):
"""
Inputs: pid (the pid of the program that called this code)
Outputs: a SIGCONT signal to the process with the matching pid
"""
if pid is not None:
system("kill -CONT " + str(pid))