任何人都可以解释一下：
让dict_list成为：
dict_list = [
{'a':1, 'b':3},
{'a':2, 'b':4}
]
然后是以下代码：
1 print('length: ' + str(len(dict_list)))
2 filtered_dict_list = filter(lambda d: d['a'] == 1, dict_list)
3 print('length: ' + str(len(list(filtered_dict_list))))
4 dict_list = list(filtered_dict_list)
5 print('length: ' + str(len(dict_list)))
将打印：
length: 2
length: 1
length: 0
dict_list在代码中永远消失了
通过切换第3和第4行：
1 print('length: ' + str(len(dict_list)))
2 filtered_dict_list = filter(lambda d: d['a'] == 1, dict_list)
3 dict_list = list(filtered_dict_list)
4 print('length: ' + str(len(list(filtered_dict_list))))
5 print('length: ' + str(len(dict_list)))
我们得到：
length: 2
length: 0
length: 1
并且可以继续使用我们过滤的dict_list
答案 0 :(得分：3)
在Python 3中，Public Sub DeleteElementAt(ByVal ArrIndex As Integer, ByRef myArr As Variant)
' this sub removes a certain element from the array, then it shrinks the size of the array by 1
Dim i As Integer
' move all element back one position
For i = ArrIndex + 1 To UBound(myArr)
myArr(i - 1) = myArr(i)
Next
' shrink the array by one, removing the last one
ReDim Preserve myArr(UBound(myArr) - 1)
End Sub
返回一个filter()对象，它是一个惰性生成器，并不会像Python 2 filter那样自动生成list对象。在您的代码中，您只需更改首先打印的结果。
filter()在第二个区块中：
1 print('length: ' + str(len(dict_list)))
2 filtered_dict_list = filter(lambda d: d['a'] == 1, dict_list)
3 print('length: ' + str(len(list(filtered_dict_list)))) # consumes filtered_dict_list
4 dict_list = list(filtered_dict_list) # attempts to consume an exhausted generator, saving an empty list
5 print('length: ' + str(len(dict_list))) # length of that empty list
这不是耗尽发电机的1 print('length: ' + str(len(dict_list)))
2 filtered_dict_list = filter(lambda d: d['a'] == 1, dict_list)
3 dict_list = list(filtered_dict_list) # consume filtered_dict_list, and *save* it
4 print('length: ' + str(len(list(filtered_dict_list)))) # attempts to consume an exhausted generator, result is empty
5 print('length: ' + str(len(dict_list))) # print the *saved* dict_list
电话;这是print()电话。如果您将list()发送至filtered_dict_list而未先将其发送至print()，则会打印list()之类的内容。