Python: List
Create List
[item_0, item_1, item_2 …]
a = [1, 2, "m"] print(a) # [1, 2, 'm']
Count Elements
len(list)
- Return the count of number of elements.
a = ["more", 4, 6] print(len(a)) # prints 3
Get a Element
list[n]
- Return element in list at index n.
a = ["more", 4, 6] print(a[1]) # prints 4
Negative index counts from right.
a = ["more", 4, 6] print(a[-1]) # prints 6
Change a Element
list[index] = new_value
- Change a element's value.
a = [1,2,3] a[2] = "b" print(a) # [1, 2, 'b']
Delete a Element
del list[index]
- Delete a element.
a = [3,4,5] del a[2] print(a) # [3, 4]
Get Sublist
list[n:m]
- Return a sublist from index n to m.
list[:m]
- From beginning to m.
list[n:]
- From n to the end, including the end element.
Warning: end index element is not included. For example, mylist[1:2]
returns only 1 elements, not 2.
x = [0, 1, 2, 3, 4, 5] print(x[1:4]) # [1, 2, 3]
Change Sublist
list[index1:index2] = new_list
- Replace a sublist by new_list.
a = [1, 2, 3, 4, 5] a[2:4] = [99, 100] print(a) # [1, 2, 99, 100, 5]
Nested Lists
Lists can be nested arbitrarily. Example:
x = [3, 4, [7, 8]]
Append extra bracket to get element of nested list.
x = [3, 4, [7, 8]] print(x[2][1]) # 8
Join 2 Lists
list1 + list2
- Join 2 lists into 1.
b = ["a", "b"] + [7, 6] print(b) # ['a', 'b', 7, 6]