human
Complete this python program:
def find_executable(program):
assistant
#Here is the Python code you requested.

    """Look through the system\s PATH looking for the specified executable
    Parameters
    program: Name of the desired executable
    Returns
    Full path to the executable (if found) or None
    """
    def is_executable(fpath):
        return (os.path.isfile(fpath) and os.access(fpath, os.X_OK))
    (fpath, fname) = os.path.split(program)
    if fpath:
        if is_executable(program):
            return program
    else:
        try:
            system_paths = os.environ['PATH']
        except KeyError:
            system_paths = '/usr/sbin:/usr/bin:/sbin:/bin:/usr/local/sbin:/usr/local/bin'
        for path in system_paths.split(os.pathsep):
            path = path.strip('"')
            exe_file = os.path.join(path, program)
            if is_executable(exe_file):
                return exe_file
    return None