Module 3 · Lists and list processing · Lesson 3 of 7
Reading and changing content
Indexing isn't just for reading. Because lists are mutable — changeable — you can also assign to a position and replace whatever's there. nums[1] = 99 swaps the second element for 99, in place, leaving everything else exactly as it was.
nums[1] = 99Only slot [1] changes — the list stays the same length, the same object.
That's a real difference from the values you've met so far. A number or a string can't be changed — you can only make a new one. A list, though, is a container you can keep rearranging without giving it a new name.
Two everyday helpers round this out: len(nums) gives the number of items, and value in nums answers a yes/no question — is that value anywhere in the list? — with a boolean. Both come up constantly. Next: making the list longer.