Values and Data Types¶

A value is one of the fundamental things — like a word or a number — that a program manipulates. The values we have seen so far are 5 (the result when we added 2 + 3), and "Hello, World!".

We can specify values directly in the programs we write. For example we can specify a number as a literal just by writing it directly, (e.g., 5 or 4.32). In a program, we specify a word, or more generally a string of characters, by enclosing the characters inside quotation marks (e.g., "Hello, World!").

During execution of a program, the python interpreter creates an internal representation of values that are specified in a program. It can then manipulate them. For example, in the next section, we’ll look at how a program can specify that values should be combined using operators like + and *. We call the internal representations objects or just values.

Normally, people don’t get to see directly what is happening when a program executes. Codelens is really useful for learning because it does make a lot of things visible during a program execution.

The print statement is also a good way to make a computed value visible to people. Each internal object has an external, printed representation. When a print statement in the program’s code says to print out the object, the printed representation appears in the output window. The printed representation of a number uses the familiar decimal representation (reading Roman Numerals is a fun challenge in museums, but thank goodness the Python interpreter doesn’t present the number 2014 as MMXIV). The printed representation of a character string is just the characters, without the quotation marks.

As you will learn in more detail later, there are some special characters, like the tab character \t and the newline character \n whose internal and external representations are different.

Numbers with a decimal point belong to a class called float, because these numbers are represented in a format called floating-point. At this stage, you can treat the words class and type interchangeably. We’ll come back to a deeper understanding of what a class is in later chapters.

You will soon encounter other types of objects as well, such as lists and dictionaries. Each of these has its own special representation for specifying an object in a program, and for displaying an object when you print it. For example, list contents are enclosed in square brackets [ ]. You will also encounter some more complicated objects that do not have very nice printed representations: printing those won’t be very useful.