Django community: RSS
This page, updated regularly, aggregates Community blog posts from the Django community.
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Why RapidSMS for SMS Application Development
Caktus has been involved in quite a few projects (Libyan voter registration, UNICEF Project Mwana, and several others) that include text messaging (a.k.a. Short Message Service, or SMS), and we always use RapidSMS as one of our tools. We've also invested our own resources in supporting and extending RapidSMS. There are other options; why do we consistently choose RapidSMS? What is RapidSMS First, what is RapidSMS? It's an open source package of useful tools that extend the Django web development framework to support processing text messages. It includes: A framework for writing code to be invoked when a text message is received and respond to it A set of backends - pluggable code modules that can interface to various ways of connecting your Django program to the phone network to pass text messages back and forth Sample applications Documentation The backends are required because unlike email, there's no universal standard for sending and receiving text messages over the Internet. Often we get access to the messages via a third party vendor, like Twilio or Tropo, that provides a proprietary interface. RapidSMS isolates us from the differences among vendors. RapidSMS is open source, under the BSD license, with UNICEF acting as … -
My approach to Class Based Views
I've written in the past about my dislike for Django's Class Based Views. Django's CBVs add a lot of complexity and verbosity, and simply get in the way of some moderately common patterns (e.g. when you have two forms in a single view). It seems I'm not alone as a Django core dev who thinks that way. In this post, however, I'll write about a different approach that I took in one project, which can be summed up like this: Write your own base class. For really simple model views, Django's own CBVs can be a time saver. For anything more complex, you will run into difficulties, and will need some heavy documentation at the very least. One solution is to use a simplified re-implementation of Class Based Views. My own approach is to go even further and start from nothing, writing your own base class, while borrowing the best ideas and incorporating only what you need. Steal the good ideas The as_view method provided by the Django's View class is a great idea — while it may not be obvious, it was hammered out after a lot of discussion as a way to help promote request isolation by creating … -
Saving processes and threads in a WSGI server with Moya
I have a webserver with 3 WSGI applications running on different domains (1, 2, 3). All deployed with a combination of Gunicorn and NGINX. A combination that works really well, but there are two annoyances that are only going to get worse the more sites I deploy: A) The configuration for each server resides in a different location on the filesystem, so I have to recall & type a long path to edit settings. B) More significantly, each server adds extra resource requirements. I follow the advice of running each WSGI application with (2 * number_of_cores + 1) processes, each with 8 threads. The threads may be overkill, but that ensures that the server can use all available capacity to handle dynamic requests. On my 4 core server, that's 9 processes, 72 threads per site. Or 27 processes, and 216 threads for the 3 sites. I suspect that is too many resources. A new feature recently added to Moya fixes both those problems. Rather than deploy a WSGI application for each site, Moya can now optionally create a single WSGI application that serves many sites. With this new system, configuration is read from /etc/moya/, which contains a directory structure like … -
Saving processes and threads in a WSGI server with Moya
I have a webserver with 3 WSGI applications running on different domains (1, 2, 3). All deployed with a combination of Gunicorn and NGINX. A combination that works really well, but there are two annoyances that are only going to get worse the more sites I deploy: A) The configuration for each server resides in a different location on the filesystem, so I have to recall & type a long path to edit settings. B) More significantly, each server adds extra resource requirements. I follow the advice of running each WSGI application with (2 * number_of_cores + 1) processes, each with 8 threads. The threads may be overkill, but that ensures that the server can use all available capacity to handle dynamic requests. On my 4 core server, that's 9 processes, 72 threads per site. Or 27 processes, and 216 threads for the 3 sites. Clearly that's not scalable if I want to host more web applications on one server. A new feature recently added to Moya fixes both those problems. Rather than deploy a WSGI application for each site, Moya can now optionally create a single WSGI application that serves many sites. With this new system, configuration is read … -
Saving processes and threads in a WSGI server with Moya
I have a webserver with 3 WSGI applications running on different domains (1, 2, 3). All deployed with a combination of Gunicorn and NGINX. A combination that works really well, but there are two annoyances that are only going to get worse the more sites I deploy: A) The configuration for each server resides in a different location on the filesystem, so I have to recall & type a long path to edit settings. B) More significantly, each server adds extra resource requirements. I follow the advice of running each WSGI application with (2 * number_of_cores + 1) processes, each with 8 threads. The threads may be overkill, but that ensures that the server can use all available capacity to handle dynamic requests. On my 4 core server, that's 9 processes, 72 threads per site. Or 27 processes, and 216 threads for the 3 sites. Clearly that's not scalable if I want to host more web applications on one server. A new feature recently added to Moya fixes both those problems. Rather than deploy a WSGI application for each site, Moya can now optionally create a single WSGI application that serves many sites. With this new system, configuration is read … -
Documenting Python without Sphinx
Last week Evennia merged its development branch with all the features mentioned in the last post. Post-merger we have since gone through and fixed remaining bugs and shortened the list at a good clip. One thing I have been considering is how to make Evennia's API auto-documenting - we are after all a MUD creation library and whereas our code has always been well-documented the docs were always only accessible from the source files themselves.Now, when you hear "Python" and "documentation" in the same sentence, the first thought usually involves Sphinx or Sphinx autodoc in some form. Sphinx produces very nice looking documentation indeed. My problem is however as follows:I don't want our API documentation to be written in a different format from the rest of our documentation, which is in Github's wiki using Markdown. Our users should be able to help document Evennia without remembering which formatting language is to be used.I don't like reStructuredText syntax. This is a personal thing. I get that it is powerful but it is also really, really ugly to read in its raw form in the source code. I feel the sources must be easy to read on their own. Sphinx plugins like … -
How to build a notification feed using Stream
Tommaso wrote a quick tutorial on how to build a notification feed using Django and Stream. How to build a notification feed using Stream. Share and Enjoy: -
Connecting Django Models with outer applications
Preface: Sometimes, parts of the data that you have to display in your application reside out of the Django models. Simple example for this is the following case - the client requires that you build them a webshop but they already have CRM solution that holds their products info. Of course they provide you with a mechanism to read this data from their CRM. Specialty: The problem is that the data in their CRM does not hold some of the product information that you need. For instance it misses SEO-friendly description and product image. So you will have to set up a model at your side and store these images there. It is easy to join them, the only thing that you will need is a simple unique key for every product. Solution: Here we use the product_id field to make the connection between the CRM data and the Django model. # in models.py class Product(models.Model): product_id = models.IntegerField(_('Original Product'), unique=True) description = models.TextField(_('SEO-friendly Description'), blank=True) pod_image = FilerImageField(verbose_name=_('Product Image'), blank=True, null=True) @property def name(self): return crm_api.get_product_name(self.product_id) # in forms.py class ProductForm(forms.ModelForm): name = forms.CharField(required=False, widget=forms.TextInput(attrs={ 'readonly': True, 'style': 'border: none'})) class Meta: model = Product widgets = { 'product_id': … -
Software for business
I am starting a new blog. The reason is that I want to keep this one more technically oriented while the other will be more business and customers oriented. Its name is Software for business and the idea is to show to the business in less technical details how the modern IT technologies like CRM & ERP systems, web sites, e-commerce solutions, online marketing and so on can help their business. If you find the topic interesting feel free to join. -
Faking attributes in Python classes...
... or how to imitate dynamic properties in a class object Preface: When you have connections between your application and other systems frequently the data is not in the most useful form for your needs. If you have an API it is awesome but sometimes it just does not act the way you want and your code quickly becomes a series of repeating API calls like api.get_product_property(product_id, property). Of course it will be easier if you can use objects to represent the data in you code so you can create something like a proxy class to this API: class Product(object): def __init__(self, product_id): self.id = product_id @property def name(self): return api_obj.get_product_property(self.id, 'name') @property def price(self): return api_obj.get_product_property(self.id, 'price') #usage product = Product(product_id) print product.name In my opinion it is cleaner, more pretty and more useful than the direct API calls. But still there is something not quite right. Problem: Your model have not two but twenty properties. Defining 20 method makes the code look not that good. Not to mention that amending the code every time when you need a new property is quite boring. So is there a better way? As I mention at the end of Connecting Django … -
Simple Site Checker
... a command line tool to monitor your sitemap links I was thinking to make such tool for a while and fortunately I found some time so here it is. Simple Site Checker is a command line tool that allows you to run a check over the links in you XML sitemap. How it works: The script requires a single attribute - a URL or relative/absolute path to xml-sitemap. It loads the XML, reads all loc-tags in it and start checking the links in them one by one. By default you will see no output unless there is an error - the script is unable to load the sitemap or any link check fails. Using the verbosity argument you can control the output, if you need more detailed information like elapsed time, checked links etc. You can run this script through a cron-like tool and get an e-mail in case of error. I will appreciate any user input and ideas so feel free to comment. -
HTTP Status Codes Site
During the development of Simple Site Checker I realised that it would be useful for test purposes if there is a website returning all possible HTTP status codes. Thanks to Google App Engine and webapp2 framework building such website was a piece of cake. The site can be found at http://httpstatuscodes.appspot.com. The home page provides a list of all HTTP status codes and their names and if you want to get an HTTP response with a specific status code just add the code after the slash, example: http://httpstatuscodes.appspot.com/200 - returns 200 OK http://httpstatuscodes.appspot.com/500 - returns 500 Internal Server Error Also at the end of each page is located the URL of the HTTP protocol Status Codes Definitions with detailed explanation for each one of them. The website code is publicly available in github at HTTP Status Codes Site. If you find it useful feel free to comment and/or share it. -
Fabric & Django
Or how automate the creation of new projects with simple script Preface: Do you remember all this tiny little steps that you have to perform every time when you start new project - create virtual environment, install packages, start and setup Django project? Kind of annoying repetition, isn't it? How about to automate it a bit. Solution: Recently I started learning Fabric and thought "What better way to test it in practice than automating a simple, repetitive task?". So, lets mark the tasks that I want the script to perform: Create virtual environment with the project name Activate the virtual environment Download list of packages and install them Make 'src' directory where the project source will reside Create new Django project in source directory Update the settings Thanks to the local command the first one was easy. The problem was with the second one. Obviously each local command is run autonomously so I had to find some way have activated virtual environment for each task after this. Fortunately the prefix context manager works like a charm. I had some issues making it read and write in the paths I wants and voilà it was working exactly as I want. The … -
Python is not a Panacea ...
... neither is any other language or framework This post was inspired by the serial discussion on the topic "Python vs other language"(in the specific case the other one was PHP, and the question was asked in a Python group so you may guess whether there are any answers in favor of PHP). It is very simple, I believe that every Python developer will tell you that Python is the greatest language ever build, how easy is to learn it, how readable and flexible it is, how much fun it is to work with it and so on. They will tell you that you can do everything with it: web and desktop development, testing, automation, scientific simulations etc. But what most of them will forgot to tell you is that it is not a Panacea. In the matter of fact you can also build "ugly" and unstable applications in Python too. Most problems come not from the language or framework used, but from bad coding practices and bad understanding of the environment. Python will force you to write readable code but it wont solve all your problems. It is hard to make a complete list of what exactly you must … -
Django compressor and image preloading
Preface: Have you noticed how on some websites when you click on a link that opens a lightbox or any overlay for first time it takes some time to display the border/background/button images. Not quite fancy, right? This is because the load of this images starts at the moment the overlay is rendered on the screen. If this is your first load and these images are not in your browser cache it will take some time for the browser to retrieve them from the server. Solution: The solution for this is to preload the images i.e. to force the browser to request them from the server before they are actually used. With a simple javascript function and a list of the images URLs this is a piece of cake: $.preLoadImages = function() { var args_len = arguments.length; for (var i=0; i < args_len; i++) { var cacheImage = document.createElement('img'); cacheImage.src = arguments[i]; } } $.preLoadImages('/img/img1.png', '/img/img2.png') Please have in mind that the code above uses the jQuery library. Specialty: Pretty easy, but you have to hardcode the URLs of all images. Also if you are using Django compressor then probably you are aware that it adds extra hash to the … -
The road to hell is paved with regular expressions ...
... or what is the cost of using regular expressions for simple tasks Regular expressions are one of the most powerful tools in computing I have ever seen. My previous post about Django compressor and image preloading is a good example how useful they might be. The only limit of their use is your imagination. But "with great power, comes great responsibility" or in this case a great cost. Even the simplest expressions can be quite heavy compared with other methods. The reason to write about this is a question recently asked in a python group. It was about how to get the elements of a list that match specific string. My proposal was to use comprehension list and simple string comparison while other member proposed using a regular expression. I was pretty sure that the regular expression is slower but not sure exactly how much slower so I made a simple test to find out. import re import timeit my_list = ['abc-123', 'def-456', 'ghi-789', 'abc456', 'abc', 'abd'] def re_check(): return [i for i in my_list if re.match('^abc$', i)] t = timeit.Timer(re_check) print 're_check result >>', re_check() print "%.2f usec/pass" % (1000000 * t.timeit(number=100000)/100000) def simple_check(): return [i for i … -
Automated deployment with Ubuntu, Fabric and Django
A few months ago I started to play with Fabric and the result was a simple script that automates the creation of a new Django project. In the last months I continued my experiments and extended the script to a full stack for creation and deployment of Django projects. As the details behind the script like the project structure that I use and the server setup are a bit long I will keep this post only on the script usage and I will write a follow up one describing the project structure and server. So in a brief the setup that I use consist of Ubuntu as OS, Nginx as web server and uWSGI as application server. The last one is controlled by Upstart. The script is available for download at GitHub. In a wait for more detailed documentation here is a short description of the main tasks and what they do: startproject:<project_name> Creates a new virtual environment Installs the predefined packages(uWSGI, Django and South)) Creates a new Django project from the predefined template Creates different configuration files for development and production environment Initializes new git repository Prompts the user to choose a database type. Then installs database required packages, … -
Django project file structure
As I promised in Automated deployment with Ubuntu, Fabric and Django I will use this post to explain the file structure that I use for my Django projects and what I benefit from it. So here is my project directory tree. The structure ~/workspace/&lt;project_name&gt;/ |-- bin |-- include |-- lib |-- local |-- src |-- .git |-- .gitignore |-- required_packages.txt |-- media |-- static |-- &lt;project_name&gt; | |-- &lt;project_name&gt; | | |-- __init__.py | | |-- settings | | | |-- __init__.py | | | |-- &lt;environment_type&gt;.py | | | |-- local.py | | |-- templates | | |-- urls.py | | |-- views.py | |-- manage.py | |-- wsgi.py |-- &lt;project_name&gt;.development.nginx.local.conf |-- &lt;project_name&gt;.&lt; environment_type&gt;.nginx.uwsgi.conf |-- &lt;project_name&gt;.&lt; environment_type&gt;.uwsgi.conf Explanation At the top I have a directory named as the project and virtual environment inside of it. The benefit from it is complete isolation of the project from the surrounding projects and python packages installed at OS level and ability to install packages without administrator permissions. It also provides an easy way to transfer the project from one system to another using a requirements file. The src folder is where I keep everything that is going to enter the version control … -
Automation, Fabric and Django - presentation
As a follow up post of Automated deployment with Ubuntu, Fabric and Django here are the slides from my presentation on topic "Automation, Fabric and Django". Unfortunately there is no audio podcast but if there is interest I can add some comments about each slide as part of this post. Automation - fabric, django and more from Ilian Iliev If there is anything that need explanation feel free to ask. -
Simple Site Checker and the User-Agent header
Preface: Nine months ago(I can't believe it was that long) I created a script called Simple Site Checker to ease the check of sitemaps for broken links. The script code if publicly available at Github. Yesterday(now when I finally found time to finish this post it must be "A few weeks ago") I decided to run it again on this website and nothing happened - no errors, no warning, nothing. Setting the output level to DEBUG showed the following message "Loading sitemap ..." and exited. Here the fault was mine, I have missed a corner case in the error catching mechanism i.e. when the sitemap URL returns something different from "200 OK" or "500 internal server error". Just a few second and the mistake was fix. Problem and Solution: I ran the script again and what a surprise the sitemap URL was returning "403 Forbidden". At the same time the sitemap was perfectly accessible via my browser. After some thinking I remembered about that some security plugins block the access to the website if there is not User-Agent header supplied. The reason for this is to block the access of simple script. In my case even an empty User-Agent did … -
Functions in Python presentation
Here is my presentation part of the in company Python course. Functions in python from Ilian Iliev The last slide - "Problem to solve" is something like a simple homework. Sample solutions will be uploaded later this week. -
Functions in Python Homework
After some delay(please excuse me for it) here are sample solutions of the problems defined in the presentation Functions in Python. Solutions are also available at GitHub. -
Introduction to Django - presentation
This presentation shows the basics of Django - what is inside the framework and explains the Model-View-Template system. One of the most important parts is a diagram how the request is processed and the response is generated. Shows the project and the application structure and the basic elements - Models, URLs dispatcher, Views and Templates. Introduction to django from Ilian Iliev -
Django for Web Prototyping
Or how to use the benefits of Django template system during the PSD to HTML phase There are two main approaches to start designing a new project - Photoshop mock-up or an HTML prototype. The first one is more traditional and well established in the web industry. The second one is more alternative and (maybe)modern. I remember a video of Jason Fried from 37 Signals where he talks about design and creativity. You can see it at http://davegray.nextslide.com/jason-fried-on-design. There he explains how he stays away from the Photoshop in the initial phase to concetrate on the things that you can interact with instead of focusing on design details. I am not planning to argue which is the better method, the important thing here is that sooner or later you get to the point where you have to start the HTML coding. Unfortunately frequently this happens in a pure HTML/CSS environment outside of the Django project and then we waste some extra amount of time to convert it to Django templates. Wouldn't be awesome if you can give the front-end developers something that they can install/run with a simple command and still to allow them to work in the Django environment … -
Python Interview Question and Answers
For the last few weeks I have been interviewing several people for Python/Django developers so I thought that it might be helpful to show the questions I am asking together with the answers. The reason is ... OK, let me tell you a story first. I remember when one of my university professors introduced to us his professor - the one who thought him. It was a really short visit but I still remember one if the things he said. "Ignorance is not bad, the bad thing is when you do no want to learn." So back to the reason - if you have at least taken care to prepare for the interview, look for a standard questions and their answers and learn them this is a good start. Answering these question may not get you the job you are applying for but learning them will give you some valuable knowledge about Python. This post will include the questions that are Python specific and I'll post the Django question separately. How are arguments passed - by reference of by value? The short answer is "neither", actually it is called "call by object” or “call by sharing"(you can check here for …
