Django community: Community blog posts RSS
This page, updated regularly, aggregates Community blog posts from the Django community.
-
Continuous integration of webapps with Buildbot
Buildbot is a powerful and flexible tool used by many sophisticated products like Python, Firefox, Webkit, Google Chrome, Twisted, Node.js and [many more](http://trac.buildbot.net/wiki/SuccessStories). Buildbot, the Continuous Integration Framework Buildbot is primarily used to build software for different architectures covering the process from code compilation to packaging, but it can also be used to do continuous integration of less sophisticated projects where tools and services like [Jenkins](http://jenkins-ci.org/) and [Travis-CI](https://travis-ci.org/) are more popular but less flexible. In this story I introduce Buildbot to run test suites for two products, a sample web application and a sample dependent web project. The web app is a fully functional open source example of a Django pluggable application. While the project is an implementation of the Django [tutorial](https://docs.djangoproject.com/en/1.5/intro/tutorial01/) plus a few simple test cases. Source code for the [app](https://github.com/danirus/django-sample-app) and the [project](https://github.com/danirus/django-sample-project) as long as the configuration files for Buildbot are available in GitHub. #### 1. The scenario The configuration will face the following final scenario: 1. Test suites for both the app and the project will run under several versions of Django and Python in order to be sure that the app is usable for every supported Django release and that the project might be ... -
Kruskal’s Algorithm
I planned to write a serious of posts on working and analysis of some of the basic algorithms. I also planned to give link to a JAVA implementation of the same. I will start off this series by first describing the Kruskal’s Algorithm for finding the cost of the Minimum Spanning Tree in a graph. Minimum Spanning Tree: A minimum cost spanning tree is a subgraph induced on the original graph such that the induced sub-graph is a tree on all the vertices on the original graph and the sum of weights of the edges on this graph is the minimum among all the possible spanning trees of the graph. The basic intuition behind the Kruskal’s algorithm is that the least weighted edge of the original graph will appear in the minimum spanning tree. Hence, sorting the edges based on their weight might be a first step in building the spanning tree. Does that mean, the first n-1 least weight edges are sufficient to build the spanning tree (If n is the number of vertices in the graph) ? We also need to ensure that the edges picked for the spanning tree do not form a cycle. Hence, that is ... -
Video and image sitemaps in Django
I recently added a sitemap to a site with many images and videos. Having the media files in the sitemap helps search engines to index them. I hadn't done this with Django before, so here are some notes. If you're not familiar with sitemaps in Django check out the official documentation and create a sitemap for a model with media files. Adding Videos To customize the output and to add videos to the default sitemap you'll want to create a custom template as described in the documentation. You can access your model instance through url.item. Here's an example for videos: {% load thumbnail %} {% for video in url.item.video_set.all %} <video:video> {% thumbnail video.image "662x372" crop="center" as thumb %} <video:thumbnail_loc>{{ MEDIA_URL }}{{ thumb }}</video:thumbnail_loc> {% endthumbnail %} <video:title>{{ url.item.title }}</video:title> {% if url.item.description %} <video:description>{{ url.item.description|striptags }}</video:description> {% endif %} <video:content_loc>{{ MEDIA_URL }}{{ video.file }}</video:content_loc> <video:publication_date>{{ url.item.pub_date|date:'c' }}</video:publication_date> <video:family_friendly>yes</video:family_friendly> <video:live>no</video:live> </video:video> {% endfor %} Include something simliar to this inside the <url> tag. I think this site uses sorl-thumbnail, so you'll probably want to modify the thumbnail section at least. One problem I had were invalid timestamps. The sitemap specs are very specific, either YYYY-MM-DD or YYYY-MM-DDThh:mm:ss+TZD. The first format ... -
Video and image sitemaps in Django
I recently added a sitemap to a site with many images and videos. Having the media files in the sitemap helps search engines to index them. I hadn't done this with Django before, so here are some notes. If you're not familiar with sitemaps in Django check out the official documentation and create a sitemap for a model with media files. Adding Videos To customize the output and to add videos to the default sitemap you'll want to create a custom template as described in the documentation. I always copy the default template from contrib/sitemaps/templates/sitemap.xml You can access your model instances through url.item. Here's an example for a video model that's connected to an item through foreign keys: {% load thumbnail %} {% for video in url.item.video_set.all %} <video:video> {% thumbnail video.image "662x372" crop="center" as thumb %} <video:thumbnail_loc>{{ MEDIA_URL }}{{ thumb }}</video:thumbnail_loc> {% endthumbnail %} <video:title>{{ url.item.title }}</video:title> {% if url.item.description %} <video:description>{{ url.item.description|striptags }}</video:description> {% endif %} <video:content_loc>{{ MEDIA_URL }}{{ video.file }}</video:content_loc> <video:publication_date>{{ url.item.pub_date|date:'c' }}</video:publication_date> <video:family_friendly>yes</video:family_friendly> <video:live>no</video:live> </video:video> {% endfor %} Include something simliar to this inside the <url> tag. I think this site uses sorl-thumbnail, so you'll probably want to modify the thumbnail section at least. One problem ... -
Video and image sitemaps in Django
I recently added a sitemap to a site with many images and videos. Having the media files in the sitemap helps search engines to index them. I hadn't done this with Django before, so here are some notes. If you're not familiar with sitemaps in Django check out the official documentation and create a sitemap for a model with media files. Adding Videos To customize the output and to add videos to the default sitemap you'll want to create a custom template as described in the documentation. I always copy the default template from contrib/sitemaps/templates/sitemap.xml You can access your model instances through url.item. Here's an example for a video model that's connected to an item through foreign keys: {% load thumbnail %} {% for video in url.item.video_set.all %} <video:video> {% thumbnail video.image "662x372" crop="center" as thumb %} <video:thumbnail_loc>{{ MEDIA_URL }}{{ thumb }}</video:thumbnail_loc> {% endthumbnail %} <video:title>{{ url.item.title }}</video:title> {% if url.item.description %} <video:description>{{ url.item.description|striptags }}</video:description> {% endif %} <video:content_loc>{{ MEDIA_URL }}{{ video.file }}</video:content_loc> <video:publication_date>{{ url.item.pub_date|date:'c' }}</video:publication_date> <video:family_friendly>yes</video:family_friendly> <video:live>no</video:live> </video:video> {% endfor %} Include something simliar to this inside the <url> tag. I think this site uses sorl-thumbnail, so you'll probably want to modify the thumbnail section at least. One problem ... -
South 0.8, Migrations and DjangoCon
A new release of an old friend, and more news on django.db.migrations. I've wanted to get a new release of South out for ages, so I'm delighted that I've finally done so. South 0.8 is now available on PyPI - there's not a great many new changes, the most notable (and the reason for the major version bump) being Python 3 support. Aymeric Augustin was instrumental in getting that support implemented, so I'd like to thank him for his work on it. On a related note, support for Python 2.5 is being dropped - if you still need that, you'll need to stick with the 0.7.x series. The other notable change is support for index_together, one of the new improvements in Django 1.5 and something that should have been released a while ago. There's still no first-party support for AUTH_USER_MODEL - it'll work fine as long as you're not distributing third-party apps with migrations. The overall solution to that is something that will have to be implemented in the rewrites that are underway. db.migrations Those rewrites are coming along well, however. Last week I was at DjangoCon EU, in Warsaw, Poland, and I had a fantastic time, as you can ... -
DjangoCon EU 2013
DjangoCon EU has always been something special. The very first European DjangoCon back in 2009 in Prague was a great start and over the years with Berlin, Amsterstam and Zurich in between in grew and grew and got better and better. This year, DjangoCon made a stop in Warsaw and, to be honest, it was the greatest conference I’ve ever been to. Back when the first plans for this year’s event started to leak I was all “what on Earth???”, but the local team and all the helpers including Ola Sitarska, Ola Sendecka, Kuba Kucharski, Tomek Paczkowski and Jarek Piotrowski made it happen: A tech conference in a park, in a tent, that worked!!! The conference Over the years, conferences did evolved into those perfectly organized events where usually only one thing breaks: the WiFi. They usually take place in perfectly AC’d hotels or conference centers and depending on the price you pay you get served hot and cold beverages by people in black & white & bow-ties. Well, DjangoCon EU has always been different being a conference by the community for the community, but this year was like off a whole different planet with the organizers taking a huge ... -
DjangoCon EU 2013
DjangoCon EU has always been something special. The very first European DjangoCon back in 2009 in Prague was a great start and over the years with Berlin, Amsterstam and Zurich in between in grew and grew and got better and better. This year, DjangoCon made a stop in Warsaw and, to be honest, it was the greatest conference I've ever been to. Back when the first plans for this year's event started to leak I was all "what on Earth???", but the local team and all the helpers including Ola Sitarska, Ola Sendecka, Kuba Kucharski, Tomek Paczkowski and Jarek Piotrowski made it happen: A tech conference in a park, in a tent, that worked!!! The conference Over the years, conferences did evolved into those perfectly organized events where usually only one thing breaks: the WiFi. They usually take place in perfectly AC'd hotels or conference centers and depending on the price you pay you get served hot and cold beverages by people in black & white & bow-ties. Well, DjangoCon EU has always been different being a conference by the community for the community, but this year was like off a whole different planet with the organizers taking a huge ... -
A Rhapsody In Warsaw
A field, a tent, and a large amount of Polish food - the makings of a great conference. DjangoCon and I have a long history. The very first DjangoCon, back in 2008, was also my very first conference - and I've achieved the slightly dubious honour of having attended every single one. They are not, of course, the only conferences that I go to; these days I try to speak at a variety of events. I've seen a lot of venues and they're all variations on a theme. That theme, of course, is large rooms full of chairs. DjangoCon EU 2013, hosted last week in Warsaw, bucked that trend and was probably the best yet - and that's not something I say lightly. Ola Sitarska and the rest of her team went for an inspired gamble that really paid off. The stage, and Craig Kersteins. From flickr.com/photos/patrick91 When I first heard of the plans to host this year's DjangoCon EU in a circus tent, I was a little sceptical - after all, conference venues have evolved over many decades to serve the many needs of a large-scale event. Seating, airflow, power, networking, A/V, catering and toilets are all needs of ... -
DjangoCon EU 2013
DjangoCon EU has always been something special. The very first European DjangoCon back in 2009 in Prague was a great start and over the years with Berlin, Amsterstam and Zurich in between in grew and grew and got better and better. This year, DjangoCon made a stop in Warsaw and, to be honest, it was the greatest conference I’ve ever been to. Back when the first plans for this year’s event started to leak I was all “what on Earth???”, but the local team and all the helpers including Ola Sitarska, Ola Sendecka, Kuba Kucharski, Tomek Paczkowski and Jarek Piotrowski made it happen: A tech conference in a park, in a tent, that worked!!! The conference Over the years, conferences did evolved into those perfectly organized events where usually only one thing breaks: the WiFi. They usually take place in perfectly AC’d hotels or conference centers and depending on the price you pay you get served hot and cold beverages by people in black & white & bow-ties. Well, DjangoCon EU has always been different being a conference by the community for the community, but this year was like off a whole different planet with the organizers taking a huge ... -
Django: Stop Writing Settings files
At this year's DjangoCon Europe I gave a Lightning talk titled "Stop Writing Settings Files". You can see the slides on SpeakerDeck. After the talk I got some interesting feedback. Some people disagree on some points for very valid reasons so I tought I'd write in more details what I was talking about. Settings across multiple environments, how do they work? A historically famous pattern is the "local_settings trick": it simply consists in adding the following lines at the end of the project's settings: try: from local_settings import * except ImportError: pass This works combined with a local_settings.py that's kept out of source control and managed manually for development-specific or production-specific settings. One issue with this technique is that it's hard to extend the base settings. If you want to add something to the value defined in the base settings, you need to copy the initial value completely. There is no way to add something to INSTALLED_APPS or MIDDLEWARE_CLASSES without redefining the value completely. To solve this problem, another pattern has emerged. Coined by Jacob Kaplan-Moss as The One True Way, it consists in reversing the import flow. Instead of importing local settings from the base settings, just import the ... -
Django 1.5 Cheat Sheet
At Mercurytide, we know all too well the difficulties of memorizing shortcuts when you work in different frameworks. Our skilled developers have created a solid, quick-start cheat sheet with an easy to reference layout. -
Django 1.5 Cheat Sheet
At Mercurytide, we know all too well the difficulties of memorizing shortcuts when you work in different frameworks. Our skilled developers have created a solid, quick-start cheat sheet with an easy to reference layout. -
Django 1.5 Cheat Sheet
At Mercurytide, we know all too well the difficulties of memorizing shortcuts when you work in different frameworks. Our skilled developers have created a solid, quick-start cheat sheet with an easy to reference layout. -
Keynote - Daniel Greenfeld
Django conferences have a tradition: there's an external luminary that gets to give a critical talk on Django. His talk won't be that. He's not external either: he wrote two scoops of Django together with Audrey (see also my review). Being critical is sometimes easy. Just bash class based views, for instance. Bashing is easy. A rant like Zed Shaw's is fun, but he's not asked because of his rants, but because of his contributions (like books). Similarly, Django delivers working stuff and that working stuff makes a lot of our work possible. So here are some good points about Django: Django is everywhere. So many people and companies use it. Django is powered by Python. Pep8, python is beautiful. And there's the import this zen of python that we use all the time to steer others and ourselves in the right direction. Django's API wins. It is understandable. No weird names: templates, views, logging, sessions. Django projects also have understandable structures. If there's no views.py or models.py or templates/ directory, you know someone messed something up. Fat models are great. Just put your business logic all on your models. They do get big this way, however. You can make ... -
Class based views: untangling the mess - Russell Keith-Magee
Russell is a Django core dev. Class based views were introduced two years ago, but they weren't greeted with universal acclaim. So he's here to clear up the mess and hopefully make it all more clear for everyone. History In the beginning of Django, there were only views. Function-based views. No generic views. Next, because of DRY, don't repeat yourself, several generic views were added. Listing objects, editing an object, for instance. Editing something happens so often that a generic view inside Django seemed like a good idea. There are some problems here, though. The configuration you can do is limited by the arguments you can give in your URL configuration. No control over the logic view. You can't pass in an alternative view. There's no re-use between views. You could "fix" this by adding more and more arguments and allow passing in callables and so, but in the end you're almost building what you'd already get with object oriented class inheritance... So... Next: class based views. It landed in Django 1.3 after it didn't work out to get it in 1.1 or 1.2. What went wrong? Then the wheels fell off. What went wrong? Fundamental confusion over purpose. There ... -
Get Django to play with old friends - Lynn Root
She works for Red Hat on http://freeipa.org, on identity stuff for Linux. Note: see her website for instructions and code examples. Say that your pointy haired boss (or customer) asks you to make an internal web app with all the buzzwords. So you can't use regular django auth, you'll need single sign on. Luckily since Django 1.5 you can have custom user models, so it'll fit with all your external requirements. One or two pieces of MIDDLEWARE_CLASSES and AUTHENTICATION_BACKENDS later and you play nice with the external single sign on. Django can be a team player. Webserver? You'll probably have to use apache. So the environment can be kerberos+apache. Add mod_auth_kerb for kerberos support. Add a "keytab" (making sure it is chown'ed to apache). There's a difference between authentication and authorization. Authentication is "just" logging in, authorization is what you're allowed to do. You'll have to connect to LDAP for that to ask which group(s) the user is a member of. Setting up your own kerberos environment (for testing) is a pain. Unless you use a ready made vagrant box for it. Instructions are on her website. -
Transactions for web developers - Aymeric Augustin
Initially he didn't know a lot about transactions, so he researched them in depth. A quote by Christophe Pettus: "transaction management tools are often made to seem like a black art". He moves from the database (postgres and sqlite) to the interface (psycopg2 and sqlite3) to the framework (django). Database A definition: an SQL transaction is a sequence of SQL statements that is atomic with respect to recovery. In SQL 92, a transaction begins with a transaction-initiating statement (almost everything can start a transaction) and it ends with a commit, an explicit rollback (ROLLBACK) or an implicit rollback. SQL 1999 changed this a bit. It has savepoints. After a savepoint, you can rollback to that savepoint, to a previous savepoint or you can set a new savepoint. Oh, and there is an explicit transaction start statement (START TRANSACTION). Key findings: Statements always run in transactions. Transactions are opened automatically. Transactions are advanced technology. Remember the dreaded "current transaction is aborted, commands ignored until end of transaction block" postgresql fault? What it actually means is "a previous statement failed, the application must perform a rollback". You cannot let postgres do any auto-recovery, that would break transactional integrity. It is your application ... -
Principle philosophy - Swift
Principle philosophy: a way to discuss our rules and beliefs that govern our actions. He tells it from his personal experience. His parents wanted to raise him as a good person. So they thought him good principles (like don't be a quitter, don't steal, etc). This is quite black/white though. We are all more gray/gray. What about the question "how can I be a good programmer"? Programmers use logic, which sounds black/white again: write tests, don't repeat yourself. Sigh. Talking about things like this is impossible without Immanuel Kant. He differentiates between reason and instinct. If "be happy" were our life goal, we'd just follow our instincts. So what is reason for, then, apart for doing good? Reason has to do with moral. There are three ways of looking at "doing good": Duty. Good things can come from duty. Duty can also lead to non-good things, though. Hm, so this is not it. Make a difference between the goal and the outcome. The outcome might be bad even though the goal could be worthy. Universal lawfullness. Only do something if you know that everybody thinks it is a good idea. Does this help with a question like "is testing good"? ... -
The advantages of diversity - Steve Holden
Open source is great. It is absolutely amazing. We live in a multi-dimensional world, though it is often presented otherwise. Some present a simple line-based worldview. Bad-Good for instance. Where do you want to be on the line? Republican-democrat? Ruby-Python? Foreigner-native? Once you think along those lines (...) you tend to start thinking in opposites. This is the basis for many invalid world views. Just draw a line, cluster according to your preference and you're ready. Linear concepts are not useful. The issue is polariation. In a one-dimensional world, there is no room for complexity. What about a Venn-diagram based worldview? It allows for a bit more subtlety, but there's still a line on the outside... The open source world has a lot to teach the rest of the world. It is focused, mostly, on outcomes and results. But it is not representative. It is not even representative of the tech industry generally. In tech, 20% are women, in open source it is more like 2%, for instance. And... we need diversity! The biggest resource in open source is people. So you'd rather not exclude many people. The most common diversity areas, to give you an idea: Ethnicity Religion Gender ... -
Does your stuff scale? - Steven Holmes
They grew from a two-person company to a 70-person one in two years. Central to that growth were Django and google app engine. Scalability means both load scalability and functional scalability. You also have to deal with organizational scalability and geographical scalability if you want to grow your organization. 1: Running Django on app engine It is easy to get confused. Is app engine real? Is it a joke? How to run your django stuff on it? Their reasons to use it: Auto-scaling. They build high-profile stuff and it needs to scale. They had a valentine day site that got a lot of attention on that day and it automatically scaled up without a change in the app. The day after it scaled down automatically, too. Services and APIs. No sysadmin needed. Some caveats with app engine: it is a sandbox. You you cannot do "pip install". The filesystem isn't there in the traditional sense; there is a blob storage instead. And it is lock-in, mostly; portability is an issue. They could work arounds these issues and ended up with a better application as a result. There are three ways (that they use) of running Django on app engine: Django ... -
Lightning talks day 3 - Djangocon.eu
html5lib Browsers are terribly forgiving. Python's parsers don't deal with everything, even valid html5 docs. html5lib was a problem. Google code and so and not python 3 compatible. The new html5lib supports python 3. Github, readthedocs, works fine! See https://pypi.python.org/pypi/html5lib Real time web - Aymeric Augustin He looked at web sockets in django. He played with tulip, Guido's library for async python. He had 1000 processes calculating a 'game of life' screen and django connected with them just fine and pushed the result to the browser. PyWaw PyWaw is a python community in Warsaw. They have now had 24 meetings with about 55 attendees. At the last meeting they even had 100 people attending. They are not alone in Poland, there are other user groups. So... go back to your cities and start user groups! Scrapy Screen scraping is when you need to get structured information from the web, quickly and with no hassle. Scrapy takes the hassle out of screen scaping. It takes away the pain of parsing horrible html. It has perfect documentation and a helpful community. You can even scrape from amazon, even including logging in. What can you do? Convert SVG to VML. Stock checker for ... -
Prehistorical Python: patterns past their prime - Lennart Regebro
Dicts This works now: >>> from collections import defaultdict >>> data = defaultdict(list) >>> data['key'].add(42) It was added in python 2.5. Previously you'd do a manual check whether the key exists and create it if it misses. Sets Sets are very useful. Sets contain unique values. Lookups are fast. Before you'd use a dictionary: >>> d = {} >>> for each in list_of_things: ... d[each] = None >>> list_of_things = d.keys() Now you'd use: >>> list_of_things = set(list_of_things) Sorting You don't need to turn a set into a list before sorting it. This works: >>> something = set(...) >>> nicely_sorted = sorted(something) Previously you'd do some_list.sort() and then turn it into a set. Sorting with cmp This one is old:: >>> def compare(x, y): ... return cmp(x.something, y.something) >>> sorted(xxxx, cmp=compare) New is to use a key. That gets you one call per item. The comparison function takes two items, so you get a whole lot of calls. Here's the new: >>> def get_key(x): ... return x.something >>> sorted(xxxx, key=get_key) Conditional expressions This one is very common! This old one is hard to debug if blank_choice also evaluates to None: >>> first_choice = include_blank and blank_choice or [] There's a ... -
Dynamic models in Django - Juergen Schackmann
The classical approach in django is: Code development You create models. Deployment Tables and columns are created with syncdb. Runtime Models and db tables are populated. This means that models are pretty much static. There is no way to modify them at runtime based on user interactions. You can get something working with for instance hstore in postgresql (see the postgresql talk). His usecase is for medical forms. The contents of those forms should be able to be defined inside the system. There are strict processes for installing medical software, so you cannot just release a new version with a new field. So you must get it to work at runtime. The solution could be to use dynamic models, models created at runtime. Sometimes configuration by subject matter experts is better than code customization by developers. Also, dynamic models reduce the number of deployment cycles. He has some criteria: Performance. Querability, which means the standard django query stuff should work. Django standard tool integration (admin, cache, and so). Supported DB backends. If possible, support all django DB backends. Complexity/maintainability. There are a couple of possible solutions: Entity attribute value (EAV) Colums are stored in separate table rows. Instead of a ... -
The path to continuous deployment - Òscar Vilaplana
If you've got continuous deployment, you've got stable servers. You make big changes in small increments. Continuous deployment forces you to do many good things: Good tests. Repeatable build. Well-configured identical machines. Automated deployment. Migrations and rollbacks Etc. Lots of good things. But let's compare it with lion taming. Originally, lions were beaten into submission, confused and kept in line with whips. Likewise you'll be beaten if you dare to touch the production machine as it might break. Now lions are understood better. Conditioning, behavior/signal mapping, reward and trust are the methods now. We understand that deployment is hard. We have behaviour/signal mapping with code/test/green/deploy. Etc. Continuous deployment: everyone is responsible. Everyone deploys. You automatically learn. Everybody uses the same environment locally for test deployments. The same as on the server. Testing is core. Slow tests are killing. Fast tests. And all types of tests: unit, functional and acceptance tests. Also automatic code checkers. The light must stay green. Quality must stay high, also test quality. You need a repeatable build. And it should include not just code, but also configuration and infrastructure. And... always follow the pipeline. Even in emergencies, follow the pipeline. Peer review, tests, and then the ...
