def METHOD_NAME(program):
    def is_exe(fpath):
        return os.path.isfile(fpath) and os.access(fpath, os.X_OK)
    for path in os.environ["PATH"].split(os.pathsep):
        exe_file = os.path.join(path, program)
        if is_exe(exe_file):
            return exe_file
    return None