safe_print.c

static void safe_print(const char *cp, int len)
{
        unsigned char   ch;
 
        if (len < 0)
                len = strlen(cp);
 
        while (len--) {
                ch = *cp++;
                if (ch > 128) {
                        fputs("M-", stdout);
                        ch -= 128;
                }
                if ((ch < 32) || (ch == 0x7f)) {
                        fputc('^', stdout);
                        ch ^= 0x40; /* ^@, ^A, ^B; ^? for DEL */
                }
                fputc(ch, stdout);
        }
}

unsafe_print.py

def unsafe_print(s):
  def repl(m):
    mode_m, mode_x, body = m.group(1, 2, 3)
    ch = ord(body)
    if mode_x:
      ch ^= 0x40
      assert ch < 32 or ch == 0x7f
    if mode_m:
      ch += 128
      assert ch > 128
    return chr(ch)
  return re.sub(r"(M-)?(\^)?(.)", repl, s)