如何将值列表转换为列表中的索引/切片？

Question

I have a list that contains many elements, where each element represents an input file, that I want to dynamically subset using the values contained within another list. For example, I have some code that dynamically generates lists that I want to use to define the sub-samples such as

[0, 1, 2, 3]

and

[1, 2, 3, 4]

But I want to use the start and end elements of each of these lists to define an slice range to be applied to another list. In other words, I want the two above lists to be converted into slices that look like this

[0:3] and [1:4]

But I don't know how to do this, and to be honest I'm not even sure the correct terminology to use to search for this. I have tried searching stack overflow for 'dynamically generate slices from lists' or even 'dynamically generate data slice' (an variants that I can think of along those lines) without any success.

Here are a few more details:

thislist = ['2019/12/26/fjjd', '2019/12/26/defg', '2020/01/09/qpfd', '2020/01/09/tosf', '2020/01/16/zpqr', '2020/01/15/zpqr', '2020/01/15/juwi']

where someIndexSlice is [0:3] and generated from a list that looks like this [0,1,2,3]

thislist[someIndexSlice] = ['2019/12/26/fjjd', '2019/12/26/defg', '2020/01/09/qpfd', '2020/01/09/tosf']

So my questions are:

1. How can I accomplish this?
2. What sort of terminology should I use to describe what I am trying to accomplish?

Thanks

Answer 1

You can use the built-in slice function:

>>> lst = [0, 1, 2, 3]
>>> as_slice = slice(lst[0], lst[-1], lst[1] - lst[0])
>>> as_slice
slice(0, 3, 1)        # which is same as [0:3]

And then to check if it works correctly:

>>> test = [1, 5, 3, 7, 8]
>>> test[as_slice]
[1, 5, 3]
>>> test[0:3]
[1, 5, 3]

NOTE: This implementation assumed your list s are equidistant, and sorted.