Extended slice that goes to beginning of sequence with negative stride
- by recursive
Bear with me while I explain my question. Skip down to the bold heading if you already understand extended slice list indexing.
In python, you can index lists using slice notation. Here's an example:
>>> A = list(range(10))
>>> A[0:5]
[0, 1, 2, 3, 4]
You can also include a stride, which acts like a "step":
>>> A[0:5:2]
[0, 2, 4]
The stride is also allowed to be negative, meaning the elements are retrieved in reverse order:
>>> A[5:0:-1]
[5, 4, 3, 2, 1]
But wait! I wanted to see [4, 3, 2, 1, 0]. Oh, I see, I need to decrement the start and end indices:
>>> A[4:-1:-1]
[]
What happened? It's interpreting -1 as being at the end of the array, not the beginning. I know you can achieve this as follows:
>>> A[4::-1]
[4, 3, 2, 1, 0]
But you can't use this in all cases. For example, in a method that's been passed indices.
My question is:
Is there any good pythonic way of using extended slices with negative strides and explicit start and end indices that include the first element of a sequence?
This is what I've come up with so far, but it seems unsatisfying.
>>> A[0:5][::-1]
[4, 3, 2, 1, 0]
