有没有办法在Python中构造惰性序列？

发布于 2024-11-15 18:44:11 字数 693 浏览 4 评论 0原文

有一个 Django 视图，它使用特定的过滤器从数据库加载 Member 对象。

现在，我需要更改此逻辑，以首先呈现特定的成员，然后让其余部分按其自然顺序排列。

最直接的方法是立即执行查询，获取列表，在开头删除并插入项目。然而，我很好奇是否还有任何方法可以利用QuerySet的惰性本质。

在 C# 中，我会这样写：

IEnumerable<Member> members = db.Members; // db.Members is lazy
members = Enumerable.Union( // construct a lazy sequence that traverses its arguments
    new [] { specificMember },
    members.Where(m => m != specificMember)
);

当循环遍历 members 时，它将首先获取 specificMember，然后使用任何原始的延迟加载逻辑 db.会员使用过。

有没有办法在 Django 和 Python 中做同样的事情？

原文

There is a Django view that loads Member objects from the database with a certain filter.

Now I need to change this logic to present a specific Member first, and let the rest follow in their natural order.

The most straightforward way is to execute the query right away, get a list, remove and insert the item at the beginning. However I am most curious if there is still any way to make use of QuerySet's lazy nature.

In C#, I would write:

IEnumerable<Member> members = db.Members; // db.Members is lazy
members = Enumerable.Union( // construct a lazy sequence that traverses its arguments
    new [] { specificMember },
    members.Where(m => m != specificMember)
);

As a loop would go through members, it would first get specificMember and then use whatever lazy loading logic original db.Members used.

Is there a way to do the same in Django and Python?

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

乱世争霸 2024-11-22 18:44:11

使用itertools.chain。类似于：

import itertools
original_members = .... # get an iterator of the data
members = itertools.chain([specific_member], original_members)

链函数返回一个迭代器。迭代器首先从第一个参数中的序列返回值，该参数是包含 Specific_member 的单元素列表。然后它开始从 original_members 返回值，我认为这是一个惰性序列。

Use itertools.chain. Something like:

import itertools
original_members = .... # get an iterator of the data
members = itertools.chain([specific_member], original_members)

The chain function returns an iterator. The iterator starts by returning the value from the sequence in the first parameter, which is a single-element list containing specific_member. Then it starts returning the values from original_members, which I assume is a lazy sequence.

回复收藏 0 原文

~没有更多了~