Making list is well and good, but we often need to change them later.
To return to the teacher/grades example: what happens when there's another test, and we need to add a new grade to the list?
There's a few ways to add onto lists in Python, depending on where we want to put the new data.
append(..) command adds whatever is in parentheses onto the end of the list.
a = ['a', 'b', 'c', 'd'] a.append(42) a --> ['a', 'b', 'c', 'd', 42]
If you want to insert an item at a specific place in a list, the
.insert(POSITION, ITEM) command looks like this:
b = ['m', 'n', 'o', 'p', 'q', 'r'] b.insert(24, 2) b --> ['m', 'n', 24, 'o', 'p', 'q', 'r'] b.insert(2, 20) b --> ['m', 'n', 20, 'o', 'p', 'q', 'r', 2]
If you use a position that's longer than the list – like the 24 above – Python inserts the item at the end of the list, rather than giving you an error.
There's two ways of extending, or adding several things onto, a list. The first uses the
extend() instruction, and the second the
When you add lists with a
+, Python "glues" the lists together:
[4,5,6] + [1,2,3] --> [4,5,6,1,2,3]
No matter how many lists you add, you'll always end up with one, comprehensive list at the end.
x = [1, 2, 3, 4] x.extend(['a', 'b', 'c']) x --> [1, 2, 3, 4, 'a', 'b', 'c']
Lists can be multiplied by numbers; when you do this, Python's actually multiplying the occurences of each element, rather than multiplying the elements themselves. For example:
[1,2] * 3 --> [1,2,1,2,1,2]  * 7 --> [7,7,7,7,7,7,7] ['c'] * 4 --> ['c','c', 'c','c']
Start with the list
li = [1, 2, 3, 4, 5] in the console below.
li = [1, 2, 3, 4, 5, "hi!"]
li = [1, 2, 3, 4, 5, "hi!", "hello!", "yo!"]