Replace a middle slice
Input
replace_slice([1,2,3,4,5], 1, 3, [9,9])
Output
[1, 9, 9, 4, 5]
Elements at indices 1 and 2 are replaced by [9,9].
Full lesson preview
Replace a sublist slice with another list
Replace a slice of a list with the contents of another list, following Python slice semantics.
Python practice20 minLists & TuplesIntermediateLast updated March 17, 2026
Problem statement
Create replace_slice(lst, start, end, replacement) that returns a new list where the slice lst[start:end] (using Python's slicing rules: start inclusive, end exclusive; start or end may be None or negative) is replaced by the elements from replacement (a list). Do not modify the original list. The function should follow Python's semantics for slices, including inserting when the slice is empty.
Task
Understand Python slice semantics and learn how to replace parts of a list safely, returning a new list.
Examples
Input format
Four arguments: a list, start index (or None), end index (or None), and a replacement list.
Output format
A new list with the specified slice replaced by the replacement contents.
Constraints
Follow Python's list slicing semantics exactly. Do not modify the input list.
Samples
Sample 1
Input
replace_slice([1,2,3], None, None, [9])
Output
[9]
Replacing the whole list with [9].