Introduction: Sequences

So far we have seen built-in types like: int, float, and str. int and float are considered to be simple or primitive or atomic data types because their values are not composed of any smaller parts. They cannot be broken down.

On the other hand, strings and lists are different from the others because they are made up of smaller pieces. In the case of strings, they are made up of smaller strings each containing one character.

Types that are comprised of smaller pieces are called collection data types. Depending on what we are doing, we may want to treat a collection data type as a single entity (the whole), or we may want to access its parts. This ambiguity is useful.

In this chapter we will examine operations that can be performed on sequences, such as picking out individual elements or subsequences (called slices) or computing their length. In addition, we’ll examine some special functions that are defined only for strings, and we’ll find out one importance difference between strings and lists, that lists can be changed (or mutated) while strings are immutable.


Strings can be defined as sequential collections of characters. This means that the individual characters that make up a string are in a particular order from left to right.

A string that contains no characters, often referred to as the empty string, is still considered to be a string. It is simply a sequence of zero characters and is represented by ‘’ or “” (two single or two double quotes with nothing in between).

Next Section - Operations on Strings