Question

我遇到了我的代码问题，一旦从列表列表中删除列表，循环就会停止运行。

data=[["why","why","hello"],["why","why","bell"],["why","hi","sllo"],["why","cry","hello"]]

for word_set in data:
    if word_set[-1]!="hello":
        data.remove(word_set)
print(data)

我想要的输出是

[['why', 'why', 'hello'], ['why', 'cry', 'hello']]

但输出是

[['why', 'why', 'hello'], ['why', 'hi', 'sllo'], ['why', 'cry', 'hello']]

如何让循环继续到列表末尾？

Answer 1

那是因为，当您删除第二个项目（其索引为1）时，它后面的项目会向前移动。在下一次迭代中，索引是2.它应该指向["why","hi","solo"]。但是，由于项目向前移动，它指向["why","cry","hello"]。这就是你得错结果的原因。

不建议在迭代列表时删除列表项。

您可以创建新列表（在第一个答案中提到）或使用filter功能。

def filter_func(item):
    if item[-1] != "hello":
        return False
    return True

new_list = filter(filter_func, old_list)

Answer 2

记住

data = [["list", "in","a list"],["list", "in","a list"],["list", "in","a list"]]
#data[0] will return ["list", "in","a list"]
#data[0][0] will return "list"
#remember that lists starts with '0' -> data[0]

Answer 3

>>> data=[["why","why","hello"],["why","why","bell"],["why","hi","sllo"],["why","cry","hello"]]
>>> y = []
>>> for subData in data:
        for dataItem in subData:
            if dataItem == "hello":
                y.append(subData)
>>> y
[['why', 'why', 'hello'], ['why', 'cry', 'hello']]

Answer 4

rand()

OR

filter(lambda x : x[-1] =="hello",[["why","why","hello"],["why","why","bell"],["why","hi","sllo"],["why","cry","hello"]])

OR

reduce(lambda x,y : x + [y] if y[-1]=="hello" else x ,[["why","why","hello"],["why","why","bell"],["why","hi","sllo"],["why","cry","hello"]],[])

Answer 5

data=[["why","why","hello"],["why","why","bell"],["why","hi","sllo"],["why","cry","hello"]]

for word_set in data[:]:
    if word_set[-1]!= "hello":
        data.remove(word_set)
print(data)

不要迭代原始数据，而是复制（data [：]）。因为从列表中删除项目时，项目的索引将发生变化。列表索引中的["why","why","bell"]是1.从数据中删除时。数据索引中的["why","hi","sllo"]将为1.下一个迭代索引为2，因此传递["why","hi","sllo"]并检查["why","cry","hello"]。

循环列表python列表

5 个答案: