c.py

#include <stdio.h>
#define print puts
#define exit return
#define pass }

#define one \
if __name__ == "__main__":
#define two "\
    """
int main(int argc, char ** argv) {
#define thr "\
    """
    print("Hello world!");
    exit(0);
pass

py.c

#include <stdio.h>
#define print puts
#define exit return
#define pass }

#define one \
if __name__ == "__main__":
#define two "\
    """
int main(int argc, char ** argv) {
#define thr "\
    """
    print("Hello world!");
    exit(0);
pass