1.1 Introduction

Data items are represented within a computer as a sequence of binary digits. These sequences can appear very similar but have different meanings since computers can store and manipulate different types of data. For example, the binary sequence

   01001100110010110101110011011100

could be a string of characters, an integer value, or a floating-point value. To distinguish between the different types of data, the term type is often used to refer to a collection of values and the term data type to refer to a given type along with a collection of operations for manipulating values of the given type.

Programming languages commonly provide data types as part of the language itself. These data types, known as primitives, come in two categories: simple and complex. The simple data types consist of values that are in the most basic form and cannot be decomposed into smaller parts. Integer and real types, for example, consist of single numeric values. The complex data types, on the other hand, are constructed of multiple components consisting of simple types or other complex types. In Python, objects, strings, lists, and dictionaries, which can contain multiple values, are all examples of complex types.

The primitive types provided by a language may not be sufficient for solving large complex problems. Thus, most languages allow for the construction of additional data types, known as user-defined types since they are defined by the programmer and not the language. Some of these data types can themselves be very complex.