[英]What do [] brackets in a for loop in python mean?
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?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? is it a case that we can't have something like this:
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 []?那么括号 [] 有什么作用呢? and why do we have x twice in
x for x in records.split....
以及为什么我们有 x 两次在
x for x in records.split....
Thanks谢谢
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: [f(x) for x in xs if condition]
的基本思想是:
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 x
or not. f(x)
可以是任何表达式,包含或不包含x
。
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
方括号 ( [] ) 通常表示 Python 中的列表。
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