It is called a sparse matrix.

Aliasing and Copying

Dictionary Operations

One way to create a dictionary is to start with the empty dictionary and add key-value pairs. The empty dictionary is denoted {}

mapping type

the last item of the list.

The dot operator

Repetition and References

Cloning Lists

a new list

If we want to modify a list and also keep a copy of the original, we need to be able to make a copy of the list itself, not just the reference. This process is sometimes called cloning,

Changes made with one alias affect the other

Because the same list has two different names, a and b, we say that it is aliased

Aliasing

a and b have the same value but do not refer to the same object.

The is operator will return true if the two references are to the same object

Objects and References

We can even insert elements into a list by squeezing them into an empty slice at the desired location

We can also remove elements from a list by assigning the empty list to them.

assignment with the slice operator

Lists are Mutable

List Slices

In Python, every object has a unique identification tag

it refers to a completely new list

Concatenation and Repetition

[56, 57, "dog"],

in and not in

List Membership

alist[2][0])

Accessing Elements

The expression inside the brackets specifies the index.

[ ]

List Length

sublists are considered to be a single item when counting the length of the list.

It is called the empty list and is denoted []

Lists are similar to strings, which are ordered collections of characters, except that the elements of a list can have any type and for any one list, the items can be of different types.