python中for循环中的[]括号是什么意思？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/30670310/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
What do [] brackets in a for loop in python mean?
提问by Mo.
I'm parsing JSON objects and found this sample line of code which I kind of understand but would appreciate a more detailed explanation of:
我正在解析 JSON 对象，并找到了这行代码示例，我有点理解但希望对以下内容进行更详细的解释：
for record in [x for x in records.split("\n") if x.strip() != '']:
I know it is spliting records to get individual records by the new line character however I was wondering why it looks so complicated? is it a case that we can't have something like this:
我知道它正在拆分记录以通过换行符获取单个记录，但是我想知道为什么它看起来如此复杂？是不是我们不能有这样的事情：
for record in records.split("\n") if x.strip() != '']:
So what do the brackets do []? and why do we have x twice in x for x in records.split....
那么括号 [] 有什么作用呢？为什么我们有两次 xx for x in records.split....
Thanks
谢谢
采纳答案by folkol
The "brackets" in your example constructs a new list from an old one, this is called list comprehension.
您示例中的“括号”从旧列表构建了一个新列表，这称为列表理解。
The basic idea with [f(x) for x in xs if condition]is:
基本思想[f(x) for x in xs if condition]是：
def list_comprehension(xs):
result = []
for x in xs:
if condition:
result.append(f(x))
return result
The f(x)can be any expression, containing xor not.
的f(x)可以是任何表达式，含有x或没有。
回答by Zizouz212
That's a list comprehension, a neat way of creating lists with certain conditions on the fly.
这是一种列表理解，一种即时创建具有特定条件的列表的巧妙方法。
You can make it a short form of this:
你可以把它变成一个简短的形式：
a = []
for record in records.split("\n"):
if record.strip() != '':
a.append(record)
for record in a:
# do something
回答by uniqueusername
The square brackets ( [] ) usually signal a list in Python.
方括号 ( [] ) 通常表示 Python 中的列表。
