In Python, a list is a mutable sequence, meaning its elements can be changed after the list is created. The standard textbook method for updating a specific element isindex assignment, which uses square brackets to select the position and the equals sign to assign a new value. For example, if nums = [10, 20, 30], then nums
[1] = 99 changes the element at index 1 from 20 to 99, producing [10, 99, 30]. This works because lists store references to objects and allow those references to be updated in-place.
Option B is incorrect because parentheses are used for function calls and tuples, and the plus sign typically performs concatenation (creating a new list) rather than modifying an existing element by position. Option C is incorrect because curly brackets denote dictionaries or sets, not lists. Option D is incorrect because del removes elements by index or slice (for example, del nums[1]), and it does not delete by "the element's value" unless you first find the index. Deleting is not the same as changing; deletion reduces the list's length and shifts later indices.
Index assignment is fundamental in list manipulation and appears in standard algorithms: updating counters, replacing sentinel values, editing collections, and implementing in-place transformations efficiently without allocating a new list.