functional.py 文件源码

def wrap_transition(op, did_change):
    """Transform operator into a transition operator.

    That is, an operator that
    only returns true if the ``did_change`` operator also returns true.

    Note:
        E.g. ``wrap_transition(operator.eq, operator.ne)`` returns function
        with signature ``(new_value, needle, old_value)`` and only returns
        true if new_value is equal to needle, but old_value was not equal
        to needle.
    """
    def compare(new_value, needle, old_value):
        return did_change(old_value, needle) and op(new_value, needle)

    return compare