Remembering days when client-server rules the world, then days when everybody praised light web clients where all user interface (UI) was prepared on web server and any user action was communicated back to server (this could lead to heavy network traffic - I've seen one mainstream ERP  program, where a change in one input, say line item quantity,  lead to several megabytes being sent over network).  I'm quite amused to see how we're returning back to thick clients and passing  more and more UI tasks back to user devices.   This probably make sense, taking into account the computing power available in user devices now (my mobile has approximately same computing power (dual core 1.2 GHz ARM CPU)  as  a reasonable  server  ten years back(Sun V240 for instance)) and  improvement of web browsers and especially their Javascript engines.   Normally utilization on an average client machine would be very low, unless client is dealing with digital media, so using  available computing  power there  is an obvious step. Network bandwidth could be now  more precious resource then client  computing cycles.

Continue reading Web Clients Are Getting Thick →

As Python is a dynamic language it offers many possibilities how to manipulate object instances during runtime.   We may for instance inject methods from another class,  achieving similar results as  if  this instance has this calls as a mix-in super class. This approach could be useful to hack some existing libraries with extra functionality, in case we have to work with created  instances.

This function will inject methods from mixin_class into instance assuring that method is properly bound to the instance.

import types

def mixin(instance, mixin_class):
    """Dynamic mixin of methods into instance - works only for new style classes"""
    for name in mixin_class.__dict__:
        if name.startswith('__') and name.endswith('__') \
        or not  type(mixin_class.__dict__[name])==types.FunctionType:
            continue

        instance.__dict__[name]=mixin_class.__dict__[name].__get__(instance)

Continue reading Dynamically Mix in Methods into An Instance in Python →

Django framework  provides integrated tests runner, which can be started by ./manage/py test (see docs for more details, key advantage of this runner is that it'll create new empty database for tests, so they do not interfere with each other or your development instance).   This tests runner runs unit tests from tests.py or models.py modules in active projects.  However in larger projects we would like to have other organization of tests code -   have for instance special test package within project that  contains many testing modules, each focused on particular aspect of the application.

Continue reading Django tests auto-discover →

It can sound bit weird, but most problematic platform for UbuntuOne client is Ubuntu itself - especially when your PC is behind proxy - or even worst when you're moving between several networks with your laptop, where some nets are using proxy.   

Continue reading UbuntuOne client behind proxy →

Often I needed to convert a set of files (audio files to different format,  text files to different encoding, ...)  in some directory structure and save results to a  new destination while retaining directory structure.   In order to walk through directory structure we can use find command,   but if we are to create output in new place, subdirectories have to be created, which is where find command line gets bit complicated (especially if we have to consider spaces in files/directories names).   So here is an example for converting text files encoding:

find . -name "*.txt" -exec bash -c 'mkdir -p "/dest-dir/`dirname "{}"`"; iconv -f utf-8 -t windows-1250 -o "/dest-dir/{}" "{}"' \;

Continue reading Converting files in directory structure →

Some types of web applications require to start long running tasks - like import of file, compilation etc., but  user still needs to have real time updates about progress of the task, eventually some error messages, warnings from the task (cannot import particular line, compilation error).   There are existing robust solutions like Celery, but it is aways fun to reinvent the wheel :-)   In this case we focus on simple solution, without need for request broker in middle, which enables  immediate/ real time updates on running tasks to client browser.

For our solution we will use two cool technologies/libraries web sockets and zeromq library.

Continue reading Long Running Taks in Web App/Django →

I do like maps.   Recently  I was looking at some digital maps and  got into more details and found several nice open source tools about which I'd like to write in this article.  As in any area open source provides interesting alternatives to work with digital maps and geographical data and what is also very interesting there are now free sources of  good quality geographical  data, which  can be used freely by everybody to create their own maps.   In this article I'm explaining how use data from Open Street Maps (OSM) project  for creating maps in QGIS and how to use PostGIS to store geographic informations and have  fun playing around with their different features of map data and tools. This tutorial is focused on linux (debian based - ubuntu 12.04 resp. mint in my case) desktop and assumes some basic knowledge of  your linux desktop administration.

Continue reading Playing with maps (QGIS, PostGIS, OSM) →

Recently I've updated TheTool to support also AppIndicator3 interface so it can show icon in Unity panel.   Although the documentation is not saying it, you can use absolute path to PNG image as icon-name ( apart of stock icon name).   I was trying to add application specific stock icons, but is somehow did not work well (only possibility is to use  xdg-icon-resource install --novendor --size 32  picture.png icon-name,   but python code for creating application specific icons with Gtk.IconFactory was not working for me - see this post on stackoverflow).

Continue reading AppIndicator3 - how to use custom icons →

While adding more capacity to my Ubuntu 12.04 based server I decided to use two disks in RAID 1 - although the whole topic is well discussed and described, it still took me some time to put all pieces together, so here I'd like to share my experiences. Plus there are couple of decision point on the way, so I'd like to explained my decisions, based on informations  I read.

Continue reading Software RAID 1 And LVM →

Recently I decided to revamp my linux HTPC and this time to do it properly - there is no disk and all media are on separate server (or NAS - I prefer server, because I'd like to run some other things there, which might be problematic to run on pure NAS box). New PC should boot from from common USB stick - 8GB - value around 5 EUR (I thought it would be more convenient to build  system and I did not have any server yet to boot from network only - actually old HTPC would become server, but first new HTPC has to be created). To overcome two major issues of common USB stick - limit on number of write operations (too much writes decrease lifetime of the stick) and slow write operations speed I decided to use overlays file system (or sometimes called union file system), where (once all system is set up) all writes go to memory - this is similar to linux live CDs or USB sticks. In order to be able to do some user customizations after installation and that user can save various data his home directory, the home directory is hosted on server/NAS and shared via NFS. The  recipe described below is for xubuntu 12.10.

Continue reading Diskless PC (booting from USB stick) with Ubuntu →