"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay." | ||
| --Sherlock Holmes - The Adventure of the Copper Beeches | ||
Everything you do with a computer is managing data. Data comes in many different shapes and flavors. It's the music you listen, the movie you stream, the PDFs you open. Even the chapter you're reading at this very moment is just a file, which is data.
Data can be simple, an integer number to represent an age, or complex, like an order placed on a website. It can be about a single object or about a collection of them.
Data can even be about data, that is, metadata. Data that describes the design of other data structures or data that describes application data or its context.
In Python, objects are abstraction for data, and Python has an amazing variety of data structures that you can use to represent data, or combine them to create your own custom data. Before we delve into the specifics, I want you to be very clear about objects in Python, so let's talk a little bit more about them.
As we already said, everything in Python is an object. But what really happens when you type an instruction like age = 42 in a Python module?
Tip
If you go to http://pythontutor.com/, you can type that instruction into a text box and get its visual representation. Keep this website in mind, it's very useful to consolidate your understanding of what goes on behind the scenes.
So, what happens is that an object is created. It gets an id, the type is set to int (integer number), and the value to 42. A name age is placed in the global namespace, pointing to that object. Therefore, whenever we are in the global namespace, after the execution of that line, we can retrieve that object by simply accessing it through its name: age.
If you were to move house, you would put all the knives, forks, and spoons in a box and label it cutlery. Can you see it's exactly the same concept? Here's a screenshot of how it may look like (you may have to tweak the settings to get to the same view):
So, for the rest of this chapter, whenever you read something such as name = some_value, think of a name placed in the namespace that is tied to the scope in which the instruction was written, with a nice arrow pointing to an object that has an id, a type, and a value. There is a little bit more to say about this mechanism, but it's much easier to talk about it over an example, so we'll get back to this later.