Python - 如何在 for 循环中使用 return 语句？

Python - How to use a return statement in a for loop?

提问by Eric.L

First of all I want to apologize for the bad title, but it was the best I could do. I tried to take a lot of screenshots to hopefully make this a little bit easier to understand.

首先，我想为糟糕的标题道歉，但这是我能做的最好的事情。我试着截取了很多截图，希望能让这更容易理解。

So I am working on a chat-bot for discord, and right now on a feature that would work as a todo-list. I have a command to add tasks to the list, where they are stored in a dict. However my problem is returning the list in a more readable format (see pictures).

所以我正在开发一个不和谐的聊天机器人，现在正在开发一个可以作为待办事项列表的功能。我有一个命令将任务添加到列表中，它们存储在字典中。但是我的问题是以更易读的格式返回列表（见图片）。

def show_todo():
    for key, value in cal.items():
        print(value[0], key)

The tasks are stored in a dictcalled cal. But in order for the bot to actually send the message I need to use a return statement, otherwise it'll just print it to the console and not to the actual chat (see pictures).

任务存储在一个dict名为cal. 但是为了让机器人真正发送消息，我需要使用 return 语句，否则它只会将其打印到控制台而不是实际聊天（见图）。

def show_todo():
    for key, value in cal.items():
        return(value[0], key)

Here is how I tried to fix it, but since I used return the for-loop does not work properly.

这是我尝试修复它的方法，但由于我使用了 return，for 循环无法正常工作。

So how do I fix this? How can I use a return statement so that it would print into the chat instead of the console?

那么我该如何解决这个问题？如何使用 return 语句使其打印到聊天中而不是控制台中？

Please see the pictuesfor a better understanding

请看图片以便更好地理解

回答by Chiheb Nexus

Using a returninside of a loop, will break it and exit the method/function even if the iteration still not finished.

使用return循环内部，即使迭代仍未完成，也会中断它并退出方法/函数。

For example:

例如：

def num():
    # Here there will be only one iteration
    # For number == 1 => 1 % 2 = 1
    # So, break the loop and return the number
    for number in range(1, 10):
        if number % 2:
            return number
>>> num()
1

In some cases/algorithms we need to break the loop if some conditions are met. However, in your current code, breaking the loop before finishing it it is an error/bad design.

在某些情况/算法中，如果满足某些条件，我们需要中断循环。但是，在您当前的代码中，在完成循环之前打破循环是错误/糟糕的设计。

Instead of that, you can use a different approach:

取而代之的是，您可以使用不同的方法：

yielding your data:

产生你的数据：

def show_todo():
    # Create a generator
    for key, value in cal.items():
        yield value[0], key

You can call it like:

你可以这样称呼它：

a = list(show_todo()) # or tuple(show_todo()) and you can iterate through it too.

Appending your data into a temporar list or tuple or dict or stringthen after the exit of your loop return your data:

将您的数据附加到临时列表或元组或字典或字符串中，然后在循环退出后返回您的数据：

def show_todo():
    my_list = []
    for key, value in cal.items():
        my_list.append([value[0], key])
    return my_list

回答by Uriel

Use a generatorsyntax (excellent explanation on SO here):

使用生成器语法（此处对 SO 的出色解释）：

def show_todo():
    for key, value in cal.items():
        yield value[0], key

for value, key in show_todo():
    print(value, key)