问题描述
what-is-the-意思-curly-大括号说它们用于词典,但是这个例子呢?
what-is-the-meaning-of-curly-braces says that they are used for dictionaries, but what about this example?
resp = {
requests.get('http://localhost:8000')
for i in range(20)
}
来自此处(实际上,它使用[]
,但它也可以与{}
一起使用).这是什么意思,为什么这个循环是颠倒的?
Taken from here (actually it uses []
, but it works with {}
as well). What is the meaning of this, and why is this loop upside-down?
推荐答案
弯括号也用于集合.这是集合理解.它创建20个requests.get
对象的集合,仅保留唯一的对象.
Curly braces are also used for sets. This is a set comprehension. It creates the set of 20 requests.get
objects, keeping only the unique ones.
如果使用[]
而不是{}
,则表示列表理解.它们是相似的,但是有两个区别
If you use []
instead of {}
it is a list comprehension. They are similar, but have two differences
- 列表是已排序
- 列表可以具有个重复元素
- the list is ordered
- the list can have duplicate elements
此外,正如您提到的,这是发出请求的一种不好的方式.理解应该用于创建列表/集合,而不是用于作为副产品调用许多命令.在这种情况下,一个简单的for循环会更好,使意图更清晰.
Also, as you mention, this is a bad way to make requests. Comprehensions should be used for creating a list/set, not for calling a number of commands as a by-product. In that case, a simple for-loop is better, it makes the intent clearer.
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