返回行结束时的语法错误 - ]

def filter_list(l):
##newList = []
##for x in l:
##    if isinstance(x, int):
##        newList.append(x)
##return newList

return [x in l if isinstance(x, int)]
                                    ^

Apologies if this is a duplicate, but I didn't see any other syntax error posts that helped. The commented code works, and the uncommented code gives me a syntax error on the last ]. I believe the list comprehension is correct, but I'm not necessarily here to ask that. Why am I getting a syntax error on the ]?

如果这是重复的道歉,但我没有看到任何其他语法错误帖子有帮助。注释的代码有效,未注释的代码在最后一段时间给出了语法错误。我相信列表理解是正确的,但我不一定要问这个。为什么我会在]上遇到语法错误?

3 个解决方案

#1

Your list comprehension syntax is incorrect. Perhaps, you meant to use (assuming l is an iterable):

您的列表推导语法不正确。也许,你打算使用(假设l是可迭代的):

[x for x in l if isinstance(x, int)]

Which is equivalent to:

这相当于:

out = []
for x in l:
    if isinstance(x, int):
        out.append(x)

#2

An easy mistake to make, but stay at it! List Comprehensions are really useful ways to help shorten code. The last line should read:

一个容易犯的错误,但坚持下去!列表理解是帮助缩短代码的有用方法。最后一行应为:

return [x for x in l if isinstance(x, int)]

#3

If you already have the explicit loop it's actually easy to convert it to a comprehension.

如果你已经有了显式循环,那么将其转换为理解就很容易了。

So if you have:

所以如果你有:

newList = []
for x in l:
    if isinstance(x, int):
        newList.append(x)

Then just remove the newlist = [] and put everything inside a [...]:

然后只需删除newlist = []并将所有内容放在[...]中:

[
for x in l:
    if isinstance(x, int):
        newList.append(x)
]

The next step is to move the actual element that is being appended at the front and remove the :

下一步是移动前面附加的实际元素并删除:

[
x
for x in l
    if isinstance(x, int)
]

That would already work, but generally you also remove the newlines:

这已经可以了,但通常你也会删除换行符:

[x for x in l if isinstance(x, int)]

At least that's how I started "learning" comprehensions, maybe it's also helpful for you.

至少这就是我开始“学习”理解的方式,也许这对你也很有帮助。

The reason why you're code throws the SyntaxError is because it looks like a "ternary" expression that is missing the else clause. The ternary looks like this:

您的代码抛出SyntaxError的原因是因为它看起来像缺少else子句的“三元”表达式。三元组看起来像这样:

expression1 if condition else expression2

In your case the expression1 is x in l, the condition is if isinstance(x, int) and you're missing the else expression2. And this "ternary" in your case would be wrapped in a list (resulting in a length-one list - if you intended that). For example:

在你的情况下,expression1是l in l,条件是if isinstance(x,int)并且你缺少else expression2。在你的情况下,这个“三元”将被包装在一个列表中(产生一个长度 - 一个列表 - 如果你打算这样做)。例如:

>>> l = [1, 2, 3]
>>> [1 in l if isinstance(1, int) else None]
[True]

#1