Sort Descending

An easy Python interview practice problem on DataDriven. Write the Python and run it against test cases, with instant feedback.

Domain
Python
Difficulty
easy
Seniority
L3

Problem

Given a list of numbers, return a new list sorted in descending order. Do not modify the input.

Biggest first. No exceptions.

Example 1

Input:

nums = [3,1,4,1,5]

Output:

[5,4,3,1,1]

Example 2

Input:

nums = [1]

Output:

[1]

Worked solution and explanation

Why this problem exists in real interviews

Sort a list without mutating the input is a one-liner that tests two specific things: do you know sorted() returns a new list and list.sort() mutates in place, and do you remember the reverse=True flag. Interviewers slip this in to check Python fluency before harder work. The single most common failure is calling nums.sort(reverse=True) and returning None implicitly.

Break down the requirements

Step 1: Use sorted() with reverse=True

sorted(nums, reverse=True) returns a new list in descending order. sorted() is the free function; list.sort() is the in-place method. The spec says 'do not modify the input,' which is the exact distinction between these two APIs.

Step 2: Return the sorted list directly

sorted() returns a list, so return its value. No need for a temporary variable, no need for .copy() (sorted already produces a new object). One expression, one return.

Step 3: Handle empty and single-element lists without special cases

sorted([]) == [] and sorted([1], reverse=True) == [1]. The Timsort implementation handles these in constant time without a branch in your code. Writing 'if not nums: return []' is a tell that you do not trust the standard library.

The solution

sorted() with reverse=True
def sort_descend(nums):
    return sorted(nums, reverse=True)

Common follow-up questions