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52 Articles

Get started with Python

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…

Get started with Python

50 ESSENTIAL PYTHON COMMANDS

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…

50 ESSENTIAL PYTHON COMMANDS

Basics 01 Running Python scripts On most of the UNIX systems, you can Python scripts from the command line. 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 other statically typed languages, you must…

Code a game of rock, paper, scissors

Resources Python 2: www.python.org/download IDLE: www.python.org/idle This tutorial will guide you through making a rock, paper, scissors game in Python. The code applies the lessons from the masterclass – and expands on what was included there – and doesn’t require any extra Python modules to run, like Pygame. Rock, paper, scissors is the perfect game to show off a little more about what exactly Python can do. Human input, comparisons, random selections and a whole host of loops are used in making a working version of the game. It’s also easy enough to adapt and expand as you see fit, adding rules and results, and even making a rudimentary AI if you wish. For this particular tutorial, we also recommend using IDLE. IDLE is a great Python IDE that is…

Code a game of rock, paper, scissors

Program a game of Hangman

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.…

Program a game of Hangman

Play poker dice using Python

Resources Python 2: www.python.org/download IDLE: www.python.org/idle So you’ve learnt how to program tic-tac-toe and guessed your way to victory at hangman. Now it’s time to head to Las Vegas and play our cards right. Or in this case, virtual dice, and more like Reno as we continue with our Python game tutorials and introduce you to some poker dice. We’re again using some of the lessons we’ve already learnt, including random number generation, list creation and modification, human input, rule setting, scoring and more. But we’ll also be adding some new skills in this tutorial. Namely, we’ll be creating and appending lists with random numbers, and using functions multiple times in one block of code to cut down on bloat. Again, we recommend using IDLE, and we’re using Python 2…

Play poker dice using Python

Create a graphical interface for Python games

Resources Python 2: www.python.org/download IDLE: www.python.org/idle The three basic games we have made in Python so far have all run in the command line or via IDLE, a Python IDE. While this allowed us to show off different ways to use Python code, we haven’t actually shown you how to present it yet. In this tutorial, we will take all three games and put them all into one neatly unified graphical interface. To this end, we’ll be making use of the small line of code we added at the bottom of each previous tutorial so we can import them as modules into our main graphical script. We’ll also modify the existing code to add some graphical elements. To do all this we’ll be using Tkinter, a default module available in…

Create a graphical interface for Python games

Bring graphics to simple Python games

Resources Python 2: www.python.org/download IDLE: www.python.org/idle We have now created a simple selector for the trio of Python games we made previously. This interface was able to launch a GUI for our rock, paper, scissors game, and run the other two in the terminal. Now, we’re going to convert the hangman and poker dice codes to work in a similar way to rock, paper, scissors. The trick with hangman comes in allowing for a different type of input, text, and the ability to have multiple rounds of the game. Tkinter allows for text entry, and we rely a lot less on ‘while’ loops to play the game in its entirety. Poker Dice needs to keep the dice analysis code, and the option to change specific dice using checkboxes. We’ll be…

Bring graphics to simple Python games

Embed Python in C

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…

Embed Python in C

Extend your Python

With the Python interpreter, you aren’t just limited to what is already available; you can extend the available functionality by defining your own Python objects, with their own methods and data, within your C code. These newly-created objects can then be called from within the Python interpreter. They are defined as static objects, with code like: The new PyObject contains the executable code for the methods to be used for your new object. You also need to create a method definition to be able to register the details with the Python interpreter. You do this by creating a PyMethodDef array: Once you have finished these two parts, you are almost ready to start using your new module code. You need to initialise it with the function: Now, you can import…

Extend your Python

System administration

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, so you shouldn’t have any excuse for not writing your own scripts. Because you will be doing a lot system…

System administration

Running subprocesses from Python

The underlying philosophy of Unix is to build small, specialised programs that do one job extremely well. You then chain these together to build more complex behaviours. There is no reason why you shouldn’t use the same philosophy within your Python scripts. There are several utility programs available to use with very little work on your part. The older way of handling this was through using functions like “popen()” and “spawnl()” from the os module, but a better way of running other programs is by using the subprocess module instead. You can then launch a program, like ls, by using: This provides you with a long file listing for the current directory. The function “run()” was introduced in Python 3.5 and is the suggested way of handling this. If you…

Running subprocesses from Python

Web development

With the content and the bulk of the computing hosted on a server, a web application can better guarantee a consistent experience for the end user. The popular Django framework provides a very complete environment of plugins and works on the DRY principle (Don’t Repeat Yourself). Because of this, you should be able to build your web application very quickly. Since Django is built on Python, you should be able to install it with “sudo pip install Django”. Most distributions should have a package for Django, too. Depending on what you want to do with your app, you may need to install a database like MySQL or postgresql to store your application data. There are Django utilities available to automatically generate a starting point for your new project’s code: This…

Web development

Other Python frameworks

While Django is one of the most popular frameworks around for doing web development, it is by no means the only one around. There are several others available that may prove to be a better fit for particular problem domains. For example, if you are looking for a really self-contained framework, you could look at web2py. Everything you need to be able to have a complete system, from databases to web servers to a ticketing system, are included as part of the framework. It is so self-contained that it can even run from a USB drive If you need even less of a framework, there are several mini-frameworks that are available. For example, CherryPy is a purely Pythonic multi-threaded web server that you can embed within your own application. This…

Computational science

Python has become one of the key languages used in science. There is a huge number of packages available to handle almost any task that you may have and, importantly, Python knows what it isn’t good at. To deal with this, Python has been designed to easily incorporate code from C or FORTRAN. This way, you can offl oad any heavy computations to more efficient code. The core package of most of the scientific code available is numpy. One of the problems in Python is that the object oriented nature of the language is the source of its inefficiencies. With no strict types, Python always needs to check parameters on every operation. Numpy provides a new datatype, the array, which helps solve some of these issues. Arrays can only hold…

Computational science

Interactive science with jupyter

For a lot of scientific problems, you need to play with your data in an interactive way. The original way you would do this was to use the Ipython web notebook. This project has since been renamed Jupyter. For those who have used a program like Mathematica or Maple, the interface should seem very familiar. Jupyter starts a server process, by default on port 8888, and then will open a web browser where you can open a worksheet. Like most other programs of this type, the entries run in chronological order, not in the order that they happen on the worksheet. This can be a bit confusing at first, but it means that if you go to edit an earlier entry, all of the following entries need to be re-executed…

Interactive science with jupyter

Robotics and electronics

Robotics is the most direct way that your code can interact with the world around you. It can read actual sensor information and move real actuators and get real work done. The first thing your robot needs is the ability to sense the world around it. The one sense that we as humans feel is most useful is sight. With web cameras being so cheap and easy to connect to hardware, vision is easy to give to your robot. The real problem is how to interpret this data. Luckily, you can use the OpenCV project to do just that. It is a vision package that can provide simple image gathering and processing, to extremely complex functions like face recognition and extraction of 3D objects. You can identify and track objects…

Robotics and electronics

ROS – Robot Operating System

While you could simply write some code that runs on a standard computer and a standard Linux distribution, this is usually not optimal when trying to handle all of the data processing that a robot needs when dealing with events in realtime. When you reach this point, you may need to look at a dedicated operating system – the Robot Operating System (ROS). ROS is designed to provide the same type of interface between running code the computer hardware it is running on, with the lowest possible overhead. One of the really powerful features of ROS is that it is designed to facilitate communication between different processes running on the computer, or potentially over multiple computers connected over some type of network. Instead of each process being a silo that…

Make extensions for XBMC with Python

Resources XBMC: www.xbmc.org/download Python 2.7x Python IDE (optional) Code on FileSilo XBMC is perhaps the most important thing that has ever happened in the open source media centre space. It started its life on the original Xbox videogames console and since then it has become the de facto software for multimedia aficionados. It also has been forked into many other successful media centre applications such as Boxee and Plex. XBMC has ultimately grown into a very powerful open source application with a solid community behind it. It supports almost all major platforms, including different hardware architectures. It is available for Linux, Windows, mac OS , Android, iOS and Raspberry Pi. In these pages we will learn to build extensions for XBMC. Extensions are a way of adding features to XBMC…

Make extensions for XBMC with Python

Scientific computing with NumPy

Resources NumPy: www.numpy.org SciPy: www.scipy.org Matplotlib: www.matplotlib.org NumPy is the primary Python package for performing scientific computing. It has a powerful N-dimensional array object, tools for integrating C/C++ and Fortran code, linear algebra, Fourier transform, and random number capabilities, among other things. NumPy also supports broadcasting, which is a clever way for universal functions to deal in a meaningful way with inputs that do not have exactly the same form. Apart from its capabilities, the other advantage of NumPy is that it can be integrated into Python programs. In other words, you may get your data from a database, the output of another program, an external file or an HTML page and then process it using NumPy. This article will show you how to install NumPy, make calculations, plot data,…

Scientific computing with NumPy

Instant messaging with Python

Resources A computer – running your favourite Linux distribution Internet connection – to access documentation Python 2.x, PyGTK and GObject – packages installed Here we’ll be implementing an instant messenger in Python with a client-server architecture. This means each client connects to the server, which relays any message that one client sends to all other clients. The server will also notify the other clients when someone joins or leaves the server. The instant messenger can work anywhere a TCP socket can: on the same computer with the loopback interface, across various computers on a LAN, or even over the internet if you were to configure your router correctly. However, our messages aren’t encrypted, so we wouldn’t recommend that. Writing an instant messenger is an interesting technical problem that covers a…

Instant messaging with Python

Bug-sweep your code with SourceClear

Resources Linux or OSX machine with internet access Python 2.7.x and pip installed on the local path www.djangoproject.com/download Git 1.9.3+ A free SourceClear.com account https://www.sourceclear.com/ The average software project today relies on dozens – sometimes hundreds – of open source libraries. Are those libraries up to date? Are there any security vulnerabilities in the versions you’re using? How would you even know? SourceClear makes it easy to answer these questions and more, automatically. You’ll get complete analysis of your open-source dependencies – security vulnerabilities, out-ofdate libraries, and license reports. To analyse your project, we’ll be using the SourceClear command-line agent. By tapping into the native build and package managers that manage opensource dependencies, we’ll start by gathering information on the full dependency graph. We’ll then match up those libraries to…

Bug-sweep your code with SourceClear

Python for system administrators

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…

Python for system administrators

Multitask with your Pi

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…

Multitask with your Pi

Threads or processes?

What if you need to actually have truly parallel code, that has the ability to run on multiple cores? Because Python has the GIL, you need to move away from using threads and go to using separate processes to handle the different tasks. Luckily, Python includes a multiprocessing module that provides the process equivalent to the threading module. As with the threading module, you create a new process object and hand in a target function to be run. You then need to call the start() method to get it running. With threads, sharing data is trivial because memory is global and everybody can see everything. However, different processes are in different memory scopes. In order to share data, we need to explicitly set up some form of communications. You can…

Use Pi to monitor audio

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…

Use Pi to monitor audio

Build tic-tac-toe with Kivy

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…

Build tic-tac-toe with Kivy

Create a two-step authentication with Twilio

Resources Python 2.7+ Flask 0.10.0: flask.pocoo.org/ Flask Github: github.com/mitsuhiko/flask A Twilio account: twilio.com Twilio’s Python REST API Helper Library: github.com/twilio/twilio-python/zipball/master MySQLDB: mysql-python.sourceforge.net Telephony is one of the most versatile technologies in our households. Despite being invented over 100 years ago, we still use the same basic infrastructure that once only carried the voices of people to deliver a rich multitude of media content at incredible speeds. As is often the case with wonderful things, they can often be complex too – and yet phones are more important now to our daily lives than ever. So, what can we do to leverage some of that versatile technology? Well, for starters we can use an API. Twilio has created a RESTful API that removes a great deal of that complexity of telephony…

Create a two-step authentication with Twilio

Part one: Program a Space Invaders clone

Resources Raspbian: www.raspberrypi.org/downloads Python: www.python.org/doc Pygame: www.pygame.org/docs When you’re learning to program in a new language or trying to master a new module, experimenting with a familiar and relatively simply project is a very useful exercise to help expand your understanding of the tools you’re using. Our Space Invaders clone is one such example that lends itself perfectly to Python and the Pygame module – it’s a simple game with almost universally understood rules and logic. While the Invaders meander their way down the screen towards you, it’s your job to pick them off while dodging their random fire. When one wave is conquered, another faster, more aggressive wave appears. We’ve tried to use many features of Pygame, which is designed to make the creation of games and interactive applications…

Part one: Program a Space Invaders clone

Part two: Add animation and sound to Pivaders

Resources Raspbian: www.raspberrypi.org/downloads Python: www.python.org/doc Pygame: www.pygame.org/docs Art assets: opengameart.org We had great fun creating our basic Space Invaders clone, Pivaders, for the previous tutorial. One of the key challenges with the project was keeping it to a manageable size – just 300 lines of Python. Without the use of Pygame’s strong set of features, that goal would likely have been overshot at least twofold. Pygame’s ability to group, manage and detect collisions thanks to the Sprite class really made a great difference to our project, not just in terms of length but in simplicity. If you missed the first part of the project, you can find the v0.1 code listing on GitHub via git.io/cBVTBg, while you can find version v0.2, including all the images, music and sound effects we…

Part two: Add animation and sound to Pivaders

Create a Minecraft Minesweeper game

Resources Jessie or Raspbian: raspberrypi.org/downloads Python: www.python.org/ You may remember or have even played the classic Minesweeper PC game that originally dates back to the 60s. Over the years it has been bundled with most operating systems, appeared on mobile phones, and even featured as a minigame variation on Super Mario Bros. This project will walk you through how to create a simple version in Minecraft: it’s Minecraft Minesweeper! You will code a program that sets out an arena of blocks and turns one of these blocks into a mine. To play the game, guide your player around the board. Each time you stand on a block you turn it to gold and collect points, but watch out for the mine as it will end the game and cover you…

Create a Minecraft Minesweeper game

Resources Pygame Zero: pygame-zero.readthedocs.org Pygame: pygame.org/download.shtml Pip pip-installer.org Python 3.2 or later www.python.org/ Code from FileSilo (optional) Games are a great way of understanding a language: you have a goal to work towards, and each feature you add brings more fun. However, games need libraries and modules for graphics and other essential games features. While the Pygame library made it relatively easy to make games in Python, it still brings in boilerplate code that you need before you get started – barriers to you or your kids getting started in coding. Pygame Zero deals with all of this boilerplate code for you, aiming to get you coding games instantly. Pg0 (as we’ll abbreviate it) makes sensible assumptions about what you’ll need for a game – from the size of the…

DEVELOP WITH PYTHON

Why? First released in 1991, companies like Google and NASA have been using Python for years Thanks to the introduction of the Web Server Gateway Interface (WSGI) in 2003, developing Python web apps for general web servers became a viable solution as opposed to restricting them to custom solutions. Python executables and installers are widely available from the official Python site at www.python.org. Mac OS X users can also benefit greatly from using Homebrew to install and manage their Python versions. Whilst OS X comes bundled with a version of Python, it has some potential drawbacks. Updating your OS may clear out any downloaded packages, and Apple’s implementation of the library differs greatly from the official release. Installing using Homebrew helps you to keep up to date and also means…

DEVELOP WITH PYTHON

01 Install Flask Create a new directory inside of which your project will live. Open a Terminal window and navigate to be inside your new directory. Create a new virtual environment for this project, placed inside a new directory called ‘venv’, and activate it. Once inside the new virtual shell, proceed to installing Flask using the ‘pip install Flask’ command. 02 Create Index Create a new file in the root of the project location called ‘index.py’. The sample API will use a SQLite database, so we need to import that module for use in the application. We’ll also import some core components from the Flask module to handle request management and response formatting as well as some other functions. The minimum import for a Flask application is Flask itself. 03…

Python in the wild

Disqus, the popular social interaction comment service provider, has been implementing their production applications in Python for a very long time. Python’s benefit for the development team was its ability to scale effectively and cater for a large number of consumers whilst also providing an effective underlying API for internal and external use. The company are now starting to run some production apps in Go, but the majority of code still runs on Python. World-renowned image sharing service Instagram and social pin board Pinterest have also implemented Python as part of their web stack, opting for Django to assist with the functionality and ability to cater for the many thousands of content views and requests made to their services. Mozilla, Atlassian’s Bitbucket repository service, and popular satire site The Onion…

Python in the wild

Django application development

Installing Django The installation of Django is 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 useful command-line…

Django application development

Hosting Python apps

Heroku heroku.com This app is perhaps one of the most wellknown cloud hosting providers. Their stack server environments support a number of core web app languages including Python as standard. Their unique Toolbelt command-line features and integration with Git repositories, as well as being incredibly quick and easy to scale and improve performance, makes them an obvious choice. A free account will let you run a Python web app on one dyno instance without any cost. Python Anywhere www.pythonanywhere.com Another hosted option, and one created specifically for Python applications in general is Python Anywhere. The free basic option plan has enough weight and power behind it to get you up and running with a Python web app without having to scale, but as soon as your project gains traction, you…

Hosting Python apps

Creating dynamic templates with Flask, Jinja2 and Twitter

Resources Python 2.7+ Flask 0.10.0: flask.pocoo.org Flask GitHub: github.com/mitsuhiko/flask A Twitter account Your favourite text editor Code downloaded from FileSilo Python and Flask are a great combination when you’re looking to handle the Twitter OAuth process and build requests to obtain tokens. We’ve used Twitter here because of the large amount of easily digestible data available on it. However, since Twitter adheres to the standards set out by OAuth 1.0, the code we’ve used to sign and build requests can be modified to work with any third-party API using the same standard without a great deal of work. For years PHP has been a mainstay of template generation, but now with welldocumented frameworks such as Flask, Sinatra and Handlebars, the ability to use powerful scripting languages greatly improves our ability…

Creating dynamic templates with Flask, Jinja2 and Twitter

Build your own blog with Django

Resources Python Source Code www.python.org/download/releases/2.7.2 Django Source Code www.djangoproject.com/download Creating your own blog always feels like a great accomplishment. Sure, you could use the fantastic WordPress if you need a complete blog with every feature you’d ever need right now. And Tumblr exists for people who just want to write something, or post pictures of corgis in space. You don’t have full control from start to finish with a prefabricated blog, though, and neither of these is written in the fantastic Django. Django is of course based on Python, the object-orientated programming language designed to have clearly readable syntax. Due to its Python base, it’s an incredibly powerful and simple-to-use language for web development with a vast array of applications. So let’s use it to make a blog. In this…

Build your own blog with Django

Deliver content to your blog

Resources Python base: http://www.python.org/download/ Django source: www.djangoproject.com/download/djangoproject.com/download/ In the last tutorial we began to build the most basic of blogs, and learned how to use a bit of Django in the process. We can now set up a new project, create a database and write basic code to read and write to the database. All simple stuff, but of course it’s core to building websites where Django might be called upon. Here we will give the front end of the site an overhaul, making it more of the standard you would expect from a modern blog. This will include a sidebar, pages, post pages and the ability to add and moderate comments. In the process we will learn some more of the benefits that come with using Django to develop…

Deliver content to your blog

Enhance your blog with extra features

Resources Python base: http://www.python.org/download/ Django source: www.djangoproject.com/download/djangoproject.com/download/ 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 RSS feed is part of a standard feed library in…

Enhance your blog with extra features

Building a Raspberry Pi Python cluster

In a previous article, we looked at how to combine multiple Raspberry Pis together to make a cluster of machines. But how can you make use of this small monster that you have created? Luckily, IPython is a great way to put all of these machines to work, getting some serious work done. IPython started out as an enhanced interface for Python, replacing the usual interactive interface that is available. The initial design involved creating a client/server system for IPython, which quickly allowed for some very interesting functionality. One of these extra capabilities is the ability to run multiple IPython servers that a single IPython client can connect to. You can then connect to these IPython servers and run processes in parallel. This first step is to install IPython on…

Building a Raspberry Pi Python cluster

Make it easier with dask

As people have worked with writing parallel Python code over time, the painful parts have been identified and people have written packages to try and make these a bit more comfortable to work with. One of these packages that has been gaining in popularity is dask. The real power of dask is its flexibility. It can use many different parallelisation backends, and it also gives methods and objects that build on those used for scientific computations. For example, these new objects can mimic numpy arrays, or pandas data frames. Because of all of this additional functionality, you can select what you want support for when you install dask. For example, if you want everything, you can install it with this command: The back end parallelisation method used by dask is…

Make it easier with dask

How to handle 3D on OpenGL

“But, what about 3D?” we hear you ask. Luckily, we can reuse much of what we have already covered here to move into three dimensions. The first change is that vertices now are defined with three values rather than two, giving you a set of x, y and z coordinates. The second change is in the category of functions that you need to use. You can see that the drawing functions used are explicitly two-dimensional in their names. For example, you should have noticed the ‘2’ in names like ‘glVertex2f()’. To draw three-dimensionally, this changes to names like ‘glVertex3fv()’. The third change is more conceptual. Once we move to three dimensions, we need to worry about where we are in relation to the object that is being drawn, and what…

How to handle 3D on OpenGL

Handle OpenGL with Pi

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…

Handle OpenGL with Pi

Turn your Raspberry Pi into a stop-motion studio

Resources Hard drive OSMC: osmc.tv/ Home network Another Linux computer, less than eight years old What have you done with your Raspberry Pi camera lately? While it gives us plenty of new ways to use the Pi, unless you’ve got your computer set up as a security webcam or you’re particularly a fan of time-lapse photography, the chances are that you’ve overlooked the Pi camera module for a while. If you’re a fan of animation or you simply want to extend the possibilities of the module, why not build a stop-motion camera? By using Python and an external button to capture images, the Raspberry Pi can actually be the perfect tool for animators. Better still, you can go beyond animating toys or bits of LEGO and go old school by…

Turn your Raspberry Pi into a stop-motion studio

Send an SMS from your Raspberry Pi

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…

Send an SMS from your Raspberry Pi

Use Pi to recognise faces

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…

Use Pi to recognise faces

Generating your own cascades

We have seen that the key part of object detection within an image is the cascade file. When you open one up, you will notice that it doesn’t seem to be very complicated. The complicated bit is in the encoded data that defines that features within the cascade algorithm that are used to identify the object. This data needs to be discovered through a training step where the relevant OpenCV functions look at images that both have the object in question and images that do not have the object. You need a much larger set of negative images compared to positive images. For example, the author of the blog entry at http:// coding-robin.de/2013/07/22/train-your-own-opencvhaar-classifier.html needed to use a set of 40 positive images and 600 negative images in order to identify…

Generating your own cascades

Hack a toy with the Raspberry Pi: Part 1

Resources An old/new toy Resistors Small disc motor LED A radio Small webcam Female-to-female jumper jerky wire Combining an old toy and a Raspberry Pi, you can embed a selection of components to create your own augmented toy that responds to user input. For example, take a £3 R2-D2 sweet dispenser, light it up, play music and stream a live web feed to your mobile device. Part one of this two-part tutorial covers setting up four basic features: an LED for the eye, a haptic motor to simulate an electric shock, a webcam stream from a hidden camera and the Star Wars theme tune broadcast to a radio. You may choose to combine these with your own hacks or use them as standalone features in other projects. Don’t feel limited…

Hack a toy with the Raspberry Pi: Part 1

Hack a toy with the Raspberry Pi: Part 2

Resources An old/new toy Resistors Small disc motor LED A radio Small webcam Female-to-female jumper jerky wire Tactile button In part one of this ‘hack a toy’ tutorial you created four hacks that were originally used to augment a £3 R2D2 sweet dispenser making it light up, vibrate, play music and stream a live web feed to a mobile device. You may have been working on your own features to use and customise your toy. Part two of this tutorial begins by showing two different ways to set up and use a button to trigger your hacks. One method is to add and code your own button, the second method is to utilise the toy’s own builtin button. The next part walks you through how to wire up, code and…

Hack a toy with the Raspberry Pi: Part 2

HOW TO USE Filesil

To access FileSilo, please visit filesilo.co.uk/bks-B56 01 Follow the on-screen instructions to create an account with our secure FileSilo system, log in and unlock the bookazine by answering a simple question about it. You can now access the content for free at any time. 02 Once you have logged in, you are free to explore the wealth of content available on FileSilo, from great video tutorials and online guides to superb downloadable resources. And the more bookazines you purchase, the more your instantly accessible collection of digital content will grow. 03 You can access FileSilo on any desktop, tablet or smartphone device using any popular browser (such as Safari, Firefox or Google Chrome). However, we recommend that you use a desktop to download content, as you may not be able…

HOW TO USE Filesil

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