Python List Methods

Python lists come with a set of built-in methods for adding, removing, searching, ordering, and copying their contents.

The built-in list methods

Because lists are mutable, most of their methods change the list in place rather than returning a new one. Knowing which methods modify the list and which return a value helps you avoid common mistakes, such as assigning the None result of an in-place method back to your variable.

MethodDescriptionReturns
append(x)Add item x to the endNone
insert(i, x)Insert item x at index iNone
extend(iter)Append all items from an iterableNone
remove(x)Remove the first item equal to xNone
pop(i)Remove and return item at index iThe removed item
clear()Remove all itemsNone
index(x)Return the index of the first item equal to xAn integer
count(x)Count how many times x appearsAn integer
sort()Sort the list in placeNone
reverse()Reverse the order in placeNone
copy()Return a shallow copy of the listA new list

Searching and counting

The index() method tells you where a value first appears, while count() reports how many times it occurs. These are read-only methods, so they never alter the list itself.

index() and count()

letters = ["a", "b", "a", "c", "a"]
print(letters.index("b"))
print(letters.count("a"))

letters.index('b') returns 1 because 'b' first appears at index 1, and letters.count('a') returns 3 because 'a' occurs three times.

Sorting and reversing

sort() and reverse()

nums = [3, 1, 4, 1, 5]
nums.sort()
print(nums)
nums.sort(reverse=True)
print(nums)

sort() rearranges the list ascending into [1, 1, 3, 4, 5], and sort(reverse=True) then orders it descending into [5, 4, 3, 1, 1]. Both change the list in place and return None.

Note: copy() makes a shallow copy: the new list is separate, but nested objects inside it are still shared. Use copy.deepcopy() when you need every nested level duplicated too.
  • In-place methods (append, sort, reverse, remove) return None, so do not assign their result back.
  • Use sorted(list) instead of list.sort() when you want a new sorted list and need to keep the original order.
  • index() and remove() raise errors if the value is missing, so check with 'in' first when unsure.

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