A Gentle Introduction to Python

”Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime.”

—Chinese proverb

Computer programming, or coding, as it is sometimes known, is telling a computer to do something using a language it understands.

Computers are very powerful tools, but unfortunately, they cannot think for themselves. They need to be told everything: how to perform a task; how to evaluate a condition to decide which path to follow; how to handle data that comes from a device, such as a network or a disk; and how to react when something unforeseen happens, in the case of, say, something being broken or missing.

You can code in many different styles and languages. Is it hard? We would say yes and no. It is a bit like writing—it is something that everybody can learn. But what if you want to become a poet? Writing alone is not enough. You have to acquire a whole other set of skills, and this will involve a longer and greater effort.

In the end, it all comes down to how far you want to go down the road. Coding is not just putting together some instructions that work. It is so much more!

Good code is short, fast, elegant, easy to read and understand, simple, easy to modify and extend, easy to scale and refactor, and easy to test. It takes time to be able to write code that has all these qualities at the same time, but the good news is that you are taking the first step toward it at this very moment by reading this book. And we have no doubt you can do it. Anyone can; in fact, we all program all the time, only we are not aware of it.

Let’s say, for example, that you want to make instant coffee. You have to get a mug, the instant coffee jar, a teaspoon, water, and a kettle. Even if you are not aware of it, you are evaluating a lot of data. You are making sure that there is water in the kettle and that the kettle is plugged in, that the mug is clean, and that there is enough coffee in the jar. Then you boil the water and, maybe in the meantime, you put some coffee in the mug. When the water is ready, you pour it into the mug, and stir.

So, how is this programming?

Well, we gathered resources (the kettle, coffee, water, teaspoon, and mug) and we verified some conditions concerning them (the kettle is plugged in, the mug is clean, and there is enough coffee). Then we started two actions (boiling the water and putting coffee in the mug), and when both of them were completed, we finally ended the procedure by pouring water into the mug and stirring.

Can you see the parallel? We have just described the high-level functionality of a coffee program. It was not that hard because this is what the brain does all day long: evaluate conditions, decide to take actions, carry out tasks, repeat some of them, and stop at some point.

All you need now is to learn how to deconstruct all those actions you do automatically in real life so that a computer can actually make some sense of them. You need to learn a language as well so that the computer can be instructed.

So, this is what this book is for. We will show you one way in which you can code successfully, and we will try to do that by means of many simple but focused examples (our favorite kind).

In this chapter, we are going to cover the following:

• Python’s characteristics and ecosystem
• Guidelines on how to get up and running with Python and virtual environments
• How to run Python programs
• How to organize Python code and its execution model