Variable data types

Variables in Python can be of a different data type. The data type of a variable is important because it specifies the kind of information that can be stored inside a variable. For example, to store numeric information, you need a variable of the numeric type. You can’t store a string in a variable designed to store numeric information. You will need to create a variable of the string type to store a string.

There are five standard data types in Python:

• numbers – used to store numeric values. Numbers can be stored as integers, long integers, floating-point values, and complex numbers. For example, the statement x = 5 will store the integer number 5 in the variable x.

• strings – used to store a contiguous set of characters. To define a string, you type the characters within single or double quotes. For example, newString = ‘This is a text’ will store that string of characters (This is a text) in the variable newString.

• lists – similar to arrays in some other programming languages, lists in Python are used to store a set of elements under a single variable name. Each element can be accesses by using its index, which is simply an address that identifies the item’s place in the list. Elements of a list are defined inside the square brackets ([]) and are separated by commas. For example. the myNumbers = [5,3,2,1] statement will define the list myNumbers with four elements. To access the first element of the list (the number 5), we can specify its index in the square brackets. Since indexes start from 0, to access the first element of the list, we would use the following statement: myNumbers[0].

• tuples – similar to lists, tuples in Python are used to store a set of elements under a single variable name. However, unlike lists, they cannot be changed once created. You can thought of tuples as read-only lists. They are used to represent fixed collections of elements, like days in the week. Elements of a tuple are defined inside the parentheses and separated by commas. For example, the myNumbers = (2,4,2,5) will create a tuple with four elements. To access the first element, we use the myNumbers[0] statement.

• dictionaries – also known as mappings, dictionaries are used to store a set of objects, but they store objects by key instead by relative position. The elements are defined within the curly braces. For example, the statement myDict = {‘color’ : ‘blue’, ‘size’ : ‘small’} will create a two word dictionary. We can access the elements of this dictionary by specifying a key. To access the value associated with the key color, we would use the following statement: myDict[‘color’].