Your suggestion doesn't work on Linux:

  $ echo 'exit 42' >xprog
  $ chmod 755 xprog
  $ python -c 'import os; os.execv("./xprog", ["./xprog"])'; echo $?
  Traceback (most recent call last):
    File "<string>", line 1, in <module>
  OSError: [Errno 8] Exec format error
  1

You don’t even need the #!, if the file doesn’t contain an interpreter at the top it’s automatically passed to /bin/sh.