的Python：功能之间传递变量 [英] Python: Passing variables between functions

问题描述

我已经花了过去几个小时阅读围绕这里和其他地方，以及实验，但我没有真正理解什么，我相信是一个很基本的概念：不同的功能之间传递的值（如变量）。

I've spent the past few hours reading around in here and elsewhere, as well as experimenting, but I'm not really understanding what I am sure is a very basic concept: passing values (as variables) between different functions.

例如，我一大堆值的一个函数分配给一个列表，然后想用在后面的另外一个新功能列表：

For example, I assign a whole bunch of values to a list in one function, then want to use that list in another function later:

list = []

def defineAList():
    list = ['1','2','3']
    print "For checking purposes: in defineAList, list is",list
    return list

def useTheList(list):
    print "For checking purposes: in useTheList, list is",list

def main():
    defineAList()
    useTheList(list)

main()

根据我的什么功能参数做什么，我希望它可以做如下理解

Based on my understanding of what function arguments do, I would expect this to do as follows:

1. 初始化名单'作为一个空列表;调用主（这一点，至少，我知道我有权利... ...）


2. 在defineAList（），分配一定的值代入名单;然后通过新的列表返回到主（）


3. 在main（）中，调用useTheList（名单）


4. 由于'名单'包含在useTheList函数的参数，我会期望useTheList现在将使用由defineAList（定义列表），而不是调用main之前定义的空列表。

不过，这显然是一个错误的认识。我的输出是：

However, this is obviously a faulty understanding. My output is:

For checking purposes: in defineAList, list is ['1', '2', '3']
For checking purposes: in useTheList, list is []

所以，因为回报，显然没有做什么，我想这样做，或至少它不会做它，我觉得它应该的方式... ...这是什么实际上做？能否请你告诉我，用这个例子中，我会做采取从defineAList（列表），并用它在useTheList（）？我倾向于更好地了解的东西，当我看到他们发生的事情，但是很多我见过的也用code正确的参数传递的例子，我不熟悉着呢，搞清楚的过程中发生了什么事对，我不是真的把这个概念的句柄。我使用的是2.7。

So, since "return" obviously does not do what I think it does, or at least it does not do it the way I think it should... what does it actually do? Could you please show me, using this example, what I would have to do to take the list from defineAList() and use it within useTheList()? I tend to understand things better when I see them happening, but a lot of the examples of proper argument-passing I've seen also use code I'm not familiar with yet, and in the process of figuring out what's going on, I'm not really getting a handle on this concept. I'm using 2.7.

在过去ETA-，问过类似的问题，有人建议我使用全局变量，而不是只是当地人。如果这将是与此有关的须─我服用类的目的，我们不允许使用全局变量。

ETA- in the past, asking a similar question, it was suggested that I use a global variable instead of just locals. If it will be relevant here also- for the purposes of the class I'm taking, we're not permitted to use globals.

感谢您！

推荐答案

这是什么是真正发生的事情：

This is what is actually happening:

global_list = []

def defineAList():
    local_list = ['1','2','3']
    print "For checking purposes: in defineAList, list is", local_list 
    return local_list 

def useTheList(passed_list):
    print "For checking purposes: in useTheList, list is", passed_list

def main():
    # returned list is ignored
    returned_list = defineAList()   

    # passed_list inside useTheList is set to global_list
    useTheList(global_list) 

main()

这是你想要什么：

def defineAList():
    local_list = ['1','2','3']
    print "For checking purposes: in defineAList, list is", local_list 
    return local_list 

def useTheList(passed_list):
    print "For checking purposes: in useTheList, list is", passed_list

def main():
    # returned list is ignored
    returned_list = defineAList()   

    # passed_list inside useTheList is set to what is returned from defineAList
    useTheList(returned_list) 

main()

您甚至可以跳过临时 returned_list 并直接将返回的值 useTheList ：

You can even skip the temporary returned_list and pass the returned value directly to useTheList:

def main():
    # passed_list inside useTheList is set to what is returned from defineAList
    useTheList(defineAList()) 

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