Python 列表理解和“不在”
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Python List Comprehension and 'not in'
提问by Nyxynyx
I'm getting started with Python and is currently learning about list comprehensions so this may sound really strange.
我刚开始使用 Python，目前正在学习列表推导式，所以这听起来可能很奇怪。
Question:Is it possible to use list comprehension to create a list of elements in tthat is not found in s?
问题：是否可以使用列表理解来创建在t中找不到的元素列表s？
I tried the following and it gave me an error:
我尝试了以下操作，但它给了我一个错误：
>>> t = [1, 2, 3, 4, 5]
>>> s = [1, 3, 5]
>>>[t for t not in s]
[t for t not in s]
^
SyntaxError: invalid syntax
采纳答案by Lucas Ribeiro
Try this:
尝试这个：
[x for x in t if x not in s]
You can nest any for if statements in list comprehensions. Try this identation, to get really long chains of conditionals, with a clearer intuition about what the code is doing.
您可以在列表推导式中嵌套任何 for if 语句。试试这个标识，以获得非常长的条件链，对代码正在做什么有更清晰的直觉。
my_list = [(x,a)
for x in t
if x not in s
if x > 0
for a in y
...]
See?
看？
回答by Leonardo.Z
[item for item in t if item not in s]
回答by MangoHands
For better efficiency, use a set:
为了提高效率，请使用一组：
mySet = set(s)
result = [x for x in t if x not in mySet]
Testing membership of a set is done is O(1), but testing membership in a list is O(n).
测试集合的成员资格是 O(1)，但测试列表中的成员资格是 O(n)。
回答by Jonathon Reinhart
I know you're asking about list comprehensions, but I wanted to point out that this specificproblem would be better accomplished using sets. The result you want is the difference of set tand s:
我知道您问的是列表推导式，但我想指出，使用s可以更好地完成这个特定问题set。你想要的结果是 sett和的差异s：
>>> t = {1,2,3,4,5}
>>> s = {1,3,5}
>>>
>>> t - s
set([2, 4])
>>>
>>> t.difference(s)
set([2, 4])
Just hoping to expand your knowledge of the tools Python provides to you.
只是希望扩展您对 Python 提供给您的工具的了解。
