Python：如何使用切片扩展列表列表？

Question

Note: python Extend will extend your given list with existing list at the end.

>>>a = [1,2,3]
>>>a.extend([4,5])
>>>[1,2,3,4,5]

How to do the same using slicing?

at 0th position, middle or somewhere else it works as expected,

>>>l = [2,4,6,8,10]
>>>l[:0] = [0, 1]
>>>l
>>>[0,1,2,4,6,8,10]

Even i have tried,

>>> l[len(l):] = [100]
>>> l
[2, 4, 6, 8, 10, 100]
>>> 

Is there better way without using function like len() ?

but at the end its insert before last value.

>>> l[-1:-1] = [100]
>>> l
[2, 4, 6, 8, 100, 10]

expected output,

>>>[2, 4, 6, 8, 10, 100]

I know using extend() method but i want to achieve using slicing at the end..

Answer 1

这是有效的，虽然它不是那样的：

l[len(l):] = [100]

Answer 2

In short, not exactly, because of how slices work (emphasis mine):

The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j . If i or j is greater than len(s) , use len(s) . If i is omitted or None , use 0 . If j is omitted or None , use len(s) . If i is greater than or equal to j , the slice is empty.

Nevertheless, note that lists actually have a maximum size, which we can find with sys.maxsize . If we use that as the start of the slice , in conjunction with the emphasised part above, we can actually do something that will work for all lists :

import sys

END = sys.MAXSIZE

a = [1, 2, 3]
b = [4, 5]

a[END:] = b
print(a)

Output:

[1, 2, 3, 4, 5]

Of course, practically speaking, just use len(a) .

Answer 3

Just use += which isn't using slicing, but is one of the ways without using an inbuilt function like len

In [1]: a = [1,2,3]                                                                                                                                                               

In [2]: a += [4,5]                                                                                                                                                                

In [3]: a                                                                                                                                                                         
Out[3]: [1, 2, 3, 4, 5]

To use slicing, the python docs already provide a solution, also noted in Amadan's answer . https://docs.python.org/3/tutorial/datastructures.html

list.extend(iterable) .
Extend the list by appending all the items from the iterable. Equivalent to a[len(a):] = iterable.

Answer 4

As per document shared by @Devesh,

Data Strutures it extend your list we need length of list.

so we can use built in function len() to do it in simple way.

otherwise we can use sys.maxsize

>>> l = [2,4,6,8,10]
>>> import sys
>>> l[sys.maxsize:] = [100, 200]
>>> l
[2, 4, 6, 8, 10, 100, 200]
>>> 

One more Solution,

Seems little better,

>>> l = [2,4,6,8,10]
>>> l[-1:] = l[-1:]+[100, 200, 300]
>>> l
[2, 4, 6, 8, 10, 100, 200, 300]
>>> 

this is another method i have tried using [].reverse() method.

>>> l = [2,4,6,8,10]
>>> l.reverse()
>>> l[:0] = [3,5,7][::-1]
>>> l
[7, 5, 3, 10, 8, 6, 4, 2]
>>> l.reverse()
>>> l
[2, 4, 6, 8, 10, 3, 5, 7]
>>>