Python: List Methods

Append to List

note: you can also join lists by list1 + list2

list.append(x)

Append x to the end.

xx = [1, 2, 3]
xx.append("a")
print(xx == [1, 2, 3, "a"])

xx = [1, 2, 3]
xx.append(["a"])
print(xx == [1, 2, 3, ["a"]])

list.extend(x)

Append x to the end, but flatten x one level if its a list.

xx = [1, 2, 3]
xx.extend(["a"])
print(xx == [1, 2, 3, "a"])

Insert an Item

list.insert(i, x)

Insert at i. Same as list[i:i] = [x]

xx = [1, 2, 3]
xx.insert(1, "a")
print(xx == [1, "a", 2, 3])

Pop, Remove First Item

list.pop()

Remove last item and return that item.

list.pop(i)

Remove ith item and return that item.

Find Item

list.index(x)

Return the index of first occurrence of x. Error if x is not in list.

xx = [0, 1, 2, 3, 4, 5, 6, 9, 8, 9]
print(xx.index(3) == 3)

list.index(x, i)

Start at index i

Best to think of index as between items. The left of first item is 0.

xx = ["a", "b", "c"]
print(xx.index("b", 1) == 1)

# print(xx.index('b', 2))
# ValueError: 'b' is not in list

list.index(x, i, j)

search between index j and j

list.remove(x)

Remove first occurrence of x. return None. Error if x is not in list.

xx = [0, 1, 2, 3]
print(xx.remove(2) == None)
print(xx == [0, 1, 3])

Find and count

list.count(x)

Return the number of occurrences of x

print([1, 2, 3, 2, 7, 2].count(2) == 3)

Sort and Reverse

Python: Sort