# from http://jimmyg.org/blog/2009/working-with-python-subprocess.html
import os


def whereis(program):
    for path in os.environ.get('PATH', '').split(':'):
        if os.path.exists(os.path.join(path, program)) and \
           not os.path.isdir(os.path.join(path, program)):
            return os.path.join(path, program)
    return None