列出Python中的简单切片？

Question

I understand slicing but i don't get why this one prints 3 ???

so here is my understanding:

it says x = [0,1,2,3,4] then

index 2 to 2 will be replaced by [0,1,2,3,4]

so x[5] is not in range

  x = range(5)
  x[2:3] = range(5)
  print x[5]

Answer 1

I think you'll undestand what's going on if you print the whole x list after doing the slice assignment. It will be [0, 1, 0, 1, 2, 3, 4, 3, 4] . The 2 from the initial range has been replaced by the whole second range, expanding the list so it will fit.

You can only expand a list with a slice assignment of this kind if the slice has a step of 1 or -1 . If you assign to a list with a larger step size, the sequence you're replacing it with has to be exactly the same size.

Answer 2

After this change...

x[2:3] = range(5)

x prints...[0, 1, 0, 1, 2, 3 , 4, 3, 4], such that the x[5] is 3 now.

Answer 3

Spilt this in parts what you are doing :

    x = range(5)

    print x

    [0, 1, 2, 3, 4]

    x[2:3] = range(5)

Here what you are doing, you want value of index x[2:3] to be range(5), Now if you print x[2:3],it will return you [2] in the list

 Print x[2:3]
 [2]

so now when you initialize x[2:3] = range(5) it will insert range(5) which is [0,1,2,3,4] in index x[2:3] that means will replace value of item 2.

After this if you print x

 x[2:3] = range(5) 
 print x
 [0, 1, 0, 1, 2, 3, 4, 3, 4]

Now if you print x[5] it will return 3 as on 5 index value is 3.

x[0] = 0
x[1] = 1
x[2] = 0
x[3] = 1
x[4] = 2
x[5] = 3
x[6] = 4
x[7] = 3
x[8] = 4

hope it helps.