问题描述
任何人都可以向我解释一下此代码段到底在做什么?
Can anyone explain to me, what exactly this code snippet is doing?
chained_country_list = set(itertools.chain.from_iterable(country_and_countrycodes)) & set(all_countries)
我知道它在彼此之间运行两个列表，最后得到一组唯一的值，该值存在于它比较的两个列表中.
I know it runs two lists against each other, ending up with a set of unique values, that exists in both the lists it compares.
但是它是如何做到的，以及幕后发生的一切使我感到困惑.
But how it does it, and whats happening under the hood, confuses me.
如果有人可以在这个问题上分享一些看法，将会有很大的帮助.
Would be a huge help if someone could share some light on the issue.
推荐答案
让我们分解代码的每个重要元素:
Let's break down each significant element of the code:
itertools.chain.from_iterable:
基本上，这用于展平嵌套列表，如下所示:
Basically, this is used to flatten a nested list, like this:
l = [[0], [1, 2], [2], [3, 6], [4], [5, 10]]
list(itertools.chain.from_iterable(l))
输出:
[0, 1, 2, 2, 3, 6, 4, 5, 10]
两组之间的
&运算符:
& operator between two sets:
请考虑以下关于集合a和b的示例.
Consider the follow example of sets a and b.
a = {1, 2, 3}
b = {2, 3, 4}
a & b
输出:
{2, 3}
因此，基本上，它获得了两个集合之间的公共元素.这是2和3.
So basically it gets the common elements between two sets. Here they're 2 and 3.
整个代码:
让我们说:
country_and_countrycodes = [('United States', 'US'), ('China', 'CH')]
all_countries = ['United States', 'Mongolia', 'Togo']
现在，第一部分是:
set(itertools.chain.from_iterable(country_and_countrycodes))
这给了我们
{'CH', 'China', 'US', 'United States'}
因此，它只是为我们从元组中获取了一个扁平集.
So, it just gets us a flat set from the tuples.
然后，第二部分是:
set(itertools.chain.from_iterable(country_and_countrycodes)) & set(all_countries)
这给了我们
{'United States'}
基本上，我们所做的是:
Basically, what we did was:
{'CH', 'China', 'US', 'United States'} & {'United States', 'Mongolia', 'Togo'}
由于这里唯一的共同元素是'United States'，所以这就是我们得到的输出.
Since the only common element here is 'United States', that's what we got as the output.
这篇关于Itertools.chain.from_iterable的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！