Python 迭代时从集合中删除项目
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delete items from a set while iterating over it
提问by skyork
I have a set myset, and I have a function which iterates over it to perform some operation on its items and this operation ultimately deletes the item from the set.
我有一个 set myset，我有一个函数，它迭代它以对其项目执行一些操作，这个操作最终从集合中删除该项目。
Obviously, I cannot do it while still iterating over the original set. I can, however, do this:
显然，我不能在仍然迭代原始集合的同时做到这一点。但是，我可以这样做：
mylist = list(myset)
for item in mylist:
# do sth
Is there any better way?
有没有更好的办法？
采纳答案by kiriloff
First, using a set, as Zero Piraeus told us, you can
首先，使用集合，正如零比雷埃夫斯告诉我们的，你可以
myset = set([3,4,5,6,2])
while myset:
myset.pop()
print(myset)
I added a printmethod giving these outputs
我添加了一个print提供这些输出的方法
>>>
set([3, 4, 5, 6])
set([4, 5, 6])
set([5, 6])
set([6])
set([])
If you want to stick to your choice for a list, I suggest you deep copy the list using a list comprehension, and loop over the copy, while removing items from original list. In my example, I make length of original list decrease at each loop.
如果你想坚持你对列表的选择，我建议你使用列表理解深度复制列表，并循环复制，同时从原始列表中删除项目。在我的示例中，我在每个循环中减少原始列表的长度。
l = list(myset)
l_copy = [x for x in l]
for k in l_copy:
l = l[1:]
print(l)
gives
给
>>>
[3, 4, 5, 6]
[4, 5, 6]
[5, 6]
[6]
[]
回答by Zero Piraeus
This ought to work:
这应该有效：
while myset:
item = myset.pop()
# do something
Or, if you need to remove items conditionally:
或者，如果您需要有条件地删除项目：
def test(item):
return item != "foo" # or whatever
myset = set(filter(test, myset))
回答by That_User
Let's return all even numbers while modifying current set.
让我们在修改当前集合时返回所有偶数。
myset = set(range(1,5))
myset = filter(lambda x:x%2==0, myset)
print myset
Will return
将返回
>>> [2, 4]
If there is opportunity use always uselambdait will make your life easier.
如果有机会使用总是使用lambda它会让你的生活更轻松。
回答by Sanjeev Kumar
Another way could be :
另一种方法可能是：
s=set()
s.add(1)
s.add(2)
s.add(3)
s.add(4)
while len(s)>0:
v=next(iter(s))
s.remove(v)
回答by Viktor Tóth
Use the copylibrary to make a copy of the set, iterate over the copy and remove from the original one. In case you want to stick to the forloop and you want to iterate over one element only once - comes in handy if you don't necessarily want to remove all the elements.
使用copy库制作集合的副本，迭代副本并从原始副本中删除。如果您想坚持for循环并且只想迭代一个元素一次 - 如果您不一定要删除所有元素，这会派上用场。
import copy
for item in copy.copy(myset):
myset.remove(item)
