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Django Baton, a cool, modern and responsive admin app

django django-admin programming

I was a happy developer using django-suit for all my working projects. Now django-suit v1 is becoming a bit oldie, it is based on bootstrap 2.3, and rewrites so many templates that its compatibility with some other apps begins to suffer (i.e. django-filer). It's a shame, it was in my opinion the best admin app overthere.

I know django-suit v2 is on stage, at the moment of this writing it is in development, and I'm quite sure it'will ...

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Images, thumbnails, entropy and PHP

php programming

Years ago' I developed a php class to create image thumbnails on the fly, evaluating the interesting part of the image. I wrote about this in my company's blog, now I'd like to share these concepts here, in my poor english.

Why, what?

Generate thumbnails from images is a common task in modern web applications, because there is no reason to serve oversized images, when they are used as 800px wide (or less) images in a template. There is no reason to make a user download the whole image (many KB or MB), if then it is resized through css.

But how to deal with thumbnails?
There are two main approaches used by modern web applications:

  1. have the backend generate ...

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Android development, fetch data from API and execute a callback

android java programming

I love first-class function programming languages (js and python for example), and I use to pass callbacks everywhere, especially when dealing with events or async tasks.

I'm a completely newbie with Java, but I started learning it because I decided time has come to develop android native applications. One of the first functionality I needed and I wanted to master is retrieving information (in json format, in my case) from some sort of API in order to display it in my application.

The equivalent in a modern js application would be making an ajax call to a server endpoint and process the data when fetched. This of course involves the use of callbacks, since data are fetched asynchronously and must ...

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Python's excess arguments

programming python

What I've always really appreciated of python is the ability to give a function an arbitrary number of positional and keyword arguments, something that in PHP is not possible and is indeed very powerful.

When declaring a function, we can define 4 different types of arguments:

  • required arguments
  • optional arguments (a default is provided)
  • excess positional arguments
  • excess keyword arguments

for example:

def myfunc(a, b=3, *c, **d)
  • a is a required argument
  • b is an optional one since it's default value it's 3
  • the single asterisk before the c argument allows the function to accept any number of positional arguments
  • the two asterisks before the d argument allow the function to support arbitrary kewyword arguments

The order of ...

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How to exclude choices of m2m raw_id_field in django admin

django django-admin programming

This procedure took a lot of effort to be understood, but now it seems quite easy.

Scenario

Imagine we need to create a recursive m2m relationship, something like a "related posts" field assigned to a Post model. It would be nice if we could exclude the current editing post from the available choices.

This is quite straightforward if we go with the default select multiple widget. In fact we only need to create a custom form class and override the queryset property of the related_posts field in the __init__ function, excluding the id of the current instance, and then assign such form class in the ModelAdmin class, see this SO question for more info.

But things become more ...

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Pretty raw_id_fields with django-salmonella and django-grappelli

django django-admin grappelli programming tips

Sometimes, when dealing with m2m relationships, we need to use the raw_id_fields property of the ModelAdmin class, in order to choose the related objects in a new page, where we can sort and filter the available items.

Without doubt the information that the widget used by django to treat such fields gives us is a bit poor. We only see the related objects's ids, it would be nicer to have the string representation of the object.

Here comes django-salmonella:

A raw_id_fields widget replacement that handles display of an object's string ...

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Add links to django admin changelist view

django django-admin programming tips

Sometimes you may need to add one or more links for each table row in your admin changelist view. There are many ways to do it, and here we'ss see a simple one. So this post is nothing more than a tip.

In my case I had to add a link opening a pdf view of the model item detail, here comes my implementation:

- app/models.py

from django.db import models
from django.core.urlresolvers import reverse
from django.utils.html import mark_safe

class MyModel(models.Model):
    title = models.CharField('title', max_length=255)
    # ...

    def pdf_link(self):
        return mark_safe('<a class="grp-button" href="%s" target="blank">view pdf</a>' % reverse('archiviocr-opera-pdf', args=[self.id]))
    pdf_link.short_description = _('PDF')

- app/admin ...

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Singleton, the PHP way

patterns php programming singleton

I realized that even if the great part of my work consists in programming PHP stuff, I rarely write about PHP in my posts, maybe because I really don't like it?

But today I'll write about a way to implement the singleton pattern with PHP.

This is quite an easy job making use of PHP 5.3.0, thanks to the "Late Static Binding" feature. In particular we'll use the get_called_class method and the static keyword. Notice that ...

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Javascript frameworks are really powerful, when you need them

javascript jquery mootools performance programming testing

Introduction

I've always used some kind of javascript framework when developing frontend stuffs. Mootools, jQuery, extjs and friends. All such frameworks provide a set of useful functionality, but above all in my opinion, they provide what is crucial for a web developer: cross browser compatibility.
The time you'll spend in writing cross browser code, even for a small project, is huge, especially if your software must support IE<9, and especially at the beginning, since you need to learn all browser ...

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Javascript event dispatcher

javascript programming

Introduction

Too much time has passed since my last post, so today I'll write about a simple javascript component, an event dispatcher which allows two entities to communicate each other.

The simplest use case I can think of is the one in which we have an object which emits an event and another object which should listen to such event.

We could implement all the stuff without the event dispatcher, but then the two entities need to be coupled in ...

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