Tabla de contenidos para The Python Book 3rd Edition en The Python Book

Python is an incredibly versatile, expansive language which, due to its similarity to everyday language, is surprisingly easy to learn even for inexperienced programmers. It has seen a huge increase in popularity since the release and rise of the Raspberry Pi, for which Python is the officially recognised programming language. In this new edition of The Python Book, you’ll find plenty of creative projects to help you get to grips with the combination of your Raspberry Pi and Python’s powerful functionality, plus lots of tutorials that focus on Python’s effectiveness away from the Raspberry Pi. You’ll learn all about how to code with Python from a standing start, with our comprehensive masterclass, then go on to complete tutorials that will consolidate your skills and help you to become fluent in…

Basics 01 Running Python scripts On most of the UNIX systems, you can run Python scripts from the command line. $ python mypyprog.py 02 Running Python programs from Python interpreter The Python interactive interpreter makes it easy to try your first steps in programming and using all Python commands. You just issue each command at the command prompt (>>>), one by one, and the answer is immediate. Python interpreter can be started by issuing the command: In this article, all the code starting at the >>> symbol is meant to be given at the Python prompt. It is also important to remember that Python takes tabs very seriously – so if you are receiving any error that mentions tabs, correct the tab spacing. 03 Dynamic typing In Java, C++, and…

Back in issue 155, we looked at how to call C functions from within a Python program to get more speed. But, there are times, within a C program, when you may want to execute some piece of Python code. Maybe you want to be able to run user code within your program, for example. This means you can enable users to use plug-ins to extend your program’s functionality. The way we can do this is by embedding Python within the C program. We will look at how to embed, how to run your Python code, and how to interact with the Python interpreter you’ve set up. This is functionality built into Python itself, so you don’t need to install anything extra on your Raspberry Pi, aside from the development…

Resources Python-devel Python development libraries, required for compiling third-party Python module setuptools setuptools allows you to download, build, install, upgrade, and uninstall Python packages with ease System administration is an important part of our computing environment. It does not matter whether you are managing systems at your work our home. Linux, being a UNIX-based operating system, already has everything a system administrator needs, such as the world-class shells (not just one but many, including Bash, csh, zsh etc), handy tools, and many other features which make the Linux system an administrator’s dream. So why do we need Python when Linux already has everything built-in? Being a dynamic scripting language, Python is very easy to read and learn. That’s just not us saying that, but many Linux distributions actually use Python…

Kivy is a highly cross-platform graphical framework for Python, designed for the creation of innovative user interfaces like multitouch apps. Its applications can run not only on the traditional desktop platforms of Linux, OS X and Windows, but also Android and iOS, plus devices like the Raspberry Pi. That means you can develop cross-platform apps using Python libraries such as Requests, SQLAlchemy or even NumPy. You can even access native mobile APIs straight from Python using some of Kivy’s sister projects. Another great feature is the Cython-optimised OpenGL graphics pipeline, allowing advanced GPU effects even though the basic Python API is very simple. Kivy is a set of Python/Cython modules that can easily be installed via pip, but you’ll need a few dependencies. It uses Pygame as a rendering backend…

By now you will know that it is possible for you to capture images using a camera and a Raspberry Pi. This lets you include image capture functionality within your own Python program, but there is so much more you can do once you add vision to your code. Here we will look at how you can add motion detection to your Python program. This kind of advanced image processing is extremely difficult to do, so we will definitely be building on the hard work of others. Specifically, we will be using the excellent OpenCV Python package. This package is constantly being improved, with more functionality being added with every update. The first thing you will need to do is install the various Python packages that you will need to…

Resources Raspberry Pi Twilio account Text messaging, or SMS (Short Message Service), has become a staple of everyday communication. What began life as a 40 pence message service is now offered by most tariff providers as an unlimited service. Twilio, a cloud communications company, enables you to send SMS messages for free from your Raspberry Pi to a mobile phone using just six lines of code. 01 Set up your Twilio account The first step of this project is to register for a Twilio account and Twilio number. This is free and will enable you to send an SMS to a registered, verified phone. Once signed up, you will receive a verification code via SMS to the registered phone. When prompted, enter this onto the Twilio site to authenticate your…

By now you will probably have played Rock, Paper, Scissors in real life. The issue with this version is that there are only three possible outcomes other than a tie. Sam Kass and Karen Bryla invented an alternative version which adds “Spock” and “lizard”. “Spock” is signified with the Star Trek Vulcan hand sign, while “lizard” is shown by forming the hand into a mouth. Spock smashes scissors and vaporises rock; he is poisoned by lizard and is disproved by paper. Lizard poisons Spock and eats paper; it is crushed by rock and decapitated by scissors. This tutorial walks you through creating your own SenseHAT version of the game. 01 How RPSLS works with the Sense HAT When you complete this tutorial you will have a folder which contains five…

Python is a great programming language for both beginners and experts. It is designed with code readability in mind, making it an excellent choice for beginners who are still getting used to various programming concepts. The language is popular and has plenty of libraries available, allowing programmers to get a lot done with relatively little code. You can make all kinds of applications in Python: you could use the Pygame framework to write simple 2D games, you could use the GTK libraries to create a windowed application, or you could try something a little more ambitious like an app such as creating one using Python’s Bluetooth and Input libraries to capture the input from a USB keyboard and relay the input events to an Android phone. For this guide we’re…

System administration Get the most out of Python in handling all of the day-to-day upkeep that keeps your system healthy System administration tasks are some of the most annoying things that you need to deal with when you have to maintain your own system. Because of this, system administrators have constantly been trying to find ways to automate these types of tasks to maximise their time. They started with basic shell scripts, and then moved on to various scripting languages. For a long time, Perl had been the language of choice for developing these types of maintenance tools. However, Python is now growing in popularity as the language to use. It has reached the point where most Linux distributions have a Python interpreter included in order to run system scripts,…

The majority of programmers will learn single-threaded programming as their first computational model. The basic idea is that instructions for the computer are processed sequentially, one after the other. This works well enough in most situations, but you will reach a point where you need to start multitasking. The classical situation for writing multi-threaded applications is to have them run on a multi-processor machine of some persuasion. In these cases, you would have some heavy, compute-bound process running on each processor. Since your Raspberry Pi is not a huge 16-core desktop machine, you might be under the assumption that you can’t take advantage of using multiple threads of execution. This isn’t true, though. There are lots of problems that map naturally to the multiple thread model. You may also have…

Installing Django The installation of Django is & migration relatively easy once you have python installed. See for yourself as we build a simple app here 01 Create Virtual Environment Create a new directory for your project and navigate inside it using a new Terminal window. Create a new virtual environment for this project, opting to use the latest Python 3. Your Python 3 location may vary, so be sure to set the correct path for the binary package. 02 Activate and Install Using your Terminal window, activate the virtual environment to start the project-specific shell. VirtualEnv has a local version of the Python package manager pip installed, so it’s fairly straight forward to run the command to install Django. 03 Create Core Project The Django install contains some incredibly…

Many of the examples we have looked at in this column have been programs that run on the console. Here we will be taking a look at how you can include 3D graphics within your Python code. The hardware on the board includes a GPU, so you should be able to take advantage of everything this computer is capable of. Since we are going to be playing with graphics, this means that you will probably want to have an actual monitor connected to your Raspberry Pi. If you don’t have one, you can connect to your Raspberry Pi over SSH with X11 forwarding turned on. As long as you have an X11 server on your desktop, you can see the display on your local machine. To get access to OpenGL…

In a previous piece, we looked at how you could use your Raspberry Pi and some Python code to look at a scene and figure out whether there was any motion there. Now we will take it one step further and see if we can get our Raspberry Pis to actually recognise faces. We’ll assume here that you are either using the camera module for the Raspberry Pi, or a USB web cam. In either case, you have a stream of images being handed to your code, ready to be processed. Again, as in previous articles, we will be using the OpenCV Python module to handle all of the heavy image processing involved. The first step is to be sure you have Python and the OpenCV module installed with: To…

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Python has a massive environment of extra modules that can provide functionality in hundreds of different disciplines. However, every programming language has a core set of functionality that everyone should know in order to get useful work done. Python is no different in this regard. Here, we will look at 50 commands that we consider to be essential to programming in Python. Others may pick a slightly different set, but this list contains the best of the best. We will cover all of the basic commands, from importing extra modules at the beginning of a program to returning values to the calling environment at the end. We will also be looking at some commands that are useful in learning about the current session within Python, like the current list of…

Resources Python 2: www.python.org/download IDLE: www.python.org/idle One of the best ways to get to know Python is by building lots of simple projects so you can understand a bit more about the programming language. This time round, we’re looking at Hangman, a multi-round game relying on if and while loops and dealing with strings of text in multiple ways. We’ll be using some of the techniques we implemented last time as well, so we can build upon them. Hangman still doesn’t require the Pygame set of modules, but it’s a little more advanced than rock-paper-scissors. We’re playing around with a lot more variables this time. However, we’re still looking at comparisons, random selections and human input, along with splitting up a string, editing a list and even displaying rudimentary graphics.…

Resources You will require a version of Python installed on your system. The good news is you don’t have to do anything to get it installed. Most of the Linux distributions already ship with either Python 2.6 or Python 2.7 We all use shell on a daily basis. For most of us, shell is the gateway into our Linux system. For years and even today, Bash has been the default shell for Linux. But it is getting a bit long in the tooth. No need to be offended: we still believe Bash is the best shell out there when compared to some other UNIX shells such as Korn Shell (KSH), C Shell (CSH) or even TCSH. This tutorial is not about Bash being incapable, but it is about how to…

With such a small physical footprint and a low power requirement, the Raspberry Pi is a perfect platform that you can use to build your own scientific equipment. We will look at how you might be able to use your Pi to monitor and analyse sounds in your environment. This is useful if you are listening for particular sounds. You need a Raspberry Pi, some kind of USB microphone, and some kind of USB wireless connection if you want to check on the monitoring process remotely. The specifics of the hardware are up to you, but you should be able to use almost anything that is available to you. This article will focus on the Python code that you will need in order to record this audio and do some…

Resources Python base: http://www.python.org/download/ Django source: https://www.djangoproject.com/download “We’re going to add summaries, excerpts and an RSS feed” We’ve been building our Django blog to create and display posts, allow people to make comments, and filter posts by month like a classic blog sidebar. We still have a bit of a way to go until it looks and behaves more like a classic blog, though. In this tutorial, we’re going to add in summaries, excerpts, categories and finally an RSS feed. This allows us to look at a few things – firstly we’ll get a better understanding of crossmodel referencing and how that works in the admin site. We will also go through how to make changes to the database, and how Django helps when creating an SQL query. Finally, the…

In November 2015, two Raspberry Pi computers were each fitted with an Astro Pi, which is an add-on board boasting an array of sensors and an 8x8 LED matrix. These were flown to the ISS and delivered to Major Tim Peake with a selection of school children’s experiments. In late December, the Astro Pi was released for sale to the public as the rebranded ‘Sense HAT’. This consists of exactly the same hardware and sensors set found on the Astro Pi but with a new ‘Sense HAT’ API. The first part of this two-part tutorial introduces you to the Sense HAT hardware and walks you through the skills required to create a Sense HAT version of the updated classic Rock, Paper, Scissors, Lizard, Spock game. These skills also stand alone…