human
Complete this python program:
def _command(name, description=None):
assistant
#Here is the Python code you requested.

    """Decorate a function used to call a command.
    If you don\t set *description*, it won\t be included in help
    (useful for deprecated commands).
    """
    def decorator(f):
        commands[name] = f
        if description:
            descriptions[name] = description
        return f
    return decorator