Three underutilized python commands

By : Shabda Raaj

Today's post are three simple Python commands which should be known more widely, but are not.

Start a simple web server to serve files from current directory.

~$ python -m SimpleHTTPServer
Serving HTTP on port 8000 ...

This is neither secure, nor scalable, but handy if you are in a directory and want to quickly test something.

Testing emails

~$ python -m smtpd -n -c DebuggingServer

Starts a fake SMTP server on port 1025. Useful if you are testing emails on a system which doesn't allow pluggable emails backends.

Pretty print JSON

echo '{"2legs":"Better", "4Legs": "Good ...

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Topics : python tips Python

The Unfuddle Tutorial

By : Shabda Raaj

Unfuddle is the tool we use for our non open source development. I have found it to be the best tool for Software Project management, in particular I think it is superior to Basecamp and Assembla.

When you start using Unfuddle, the number of things can seem overwhelming. This tutorial should help you Unfuddle the Unfuddle.

The Unfuddle Glossary

Unfuddle has,

  • Projects: Top level Things which need to be done.
  • User: People who are working on a given project.
  • Ticket: What a User works on.
  • Milestone: A timed list of tickets which should be completed before this given time ...

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Topics : tips tutorial

Tools of Pro Django developer - aka What powers dinette and almost every app we write.

By : Shabda Raaj

There are some tools and apps which we use with almost all apps we write, and in particular which, we used for dinette. Here they are broken into useful during development, and (also) useful post development.

During Development

  1. Ipython and ipdb
  2. South
  3. Django test utils
  4. Django extensions
  5. Django debug toolbar
Ipython and ipdb

Ipython is a enhanced shell for python. Ipdb similarly add extra capacity to the builtin pdb debugger. It is extremely convenient to drop into a ipython shell right where a complex piece of code is being hit.

from IPython.Shell import IPShellEmbed
ipython = IPShellEmbed()

Of course ...

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Topics : python tips

Using bpython shell with django (and some Ipython features you should know)

By : lakshman

What is bpython?

bpython is a fancy interface to the Python interpreter for Unix-like operating system.

says the bpython home page. It provides syntax highlighting, auto completion, auto-indentation and such stuff.

Unlike iPython, which implements then entire shell functions and emulates the standard python shell, and adds enhancements, bpython just adds features on top of the existing python shell functionality, using the curses module.


The "killer feature" of bpython is, as you can see from the image above, the IDE like prompting of the function parameters and the doc string of the function dynamically. I have always thought, what IntellijIDEA ...

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Django quiz

By : Shabda Raaj

A quick django quiz. Answers available tomorrow. Get it as a text file (django-quiz) or on google docs or read below.

### Easy

1. You have a class defined as

    class Post(models.Model):
        name = models.CharField(max_length=100)
        is_active = models.BooleanField(default=False)

You create multiple objects of this type. If you do

what exceptions is raised?

a. MultipleObjectsReturned
b. ManyObjectsReturned
c. SyntaxError
d. MultipleModelReturned
e. ManyModelReturned

2. Where is the function render_to_response defined?

a. django.views
b. django.shortcuts
c. django.templates
d. django.contrib.templates
e. django.contrib.shortcuts

3. What is the ...

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Topics : django tips meta

Writing your own template loaders

By : Shabda Raaj

Django has three builtin template loaders which are used to get the templates for rendering.

#     'django.template.loaders.eggs.load_template_source',

Writing your template loader is a awfuly easy. It is a callable which

  1. Returns a tuple of (openfile, filename) if it can find the template.
  2. Raise TemplateDoesNotExist if the templates cannot be found.

The simplest template loader can be

from django.template import TemplateDoesNotExist
def load_template_source(template_name, template_dirs=None):
            return open(template_name).read(), template_name
        except IOError:
            raise TemplateDoesNotExist, template_name

if you put this to your template loaders directory ...

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A response to Dropping Django

By : Shabda Raaj

Brandon Bloom yesterday wrote an interesting post titled dropping Django. Despite a lot of hand waving(We needed a pragmatic template language to replace Django's idealistic one.), it raises some valid questions, so here is a solution to some of them.

No support for hierarchical url creation.

The simplest representation of nested urls I can think of is a nested tuple. Lets represent, the urls for a simple app by,

>>> tree_urls = ('', 'list',
...     ('edit/', 'edit', ('auto/', 'edit_auto')),
...     ('^add/', 'add'),
...     ('delete/', 'delete', ('hard/', 'delete_hard'))
...     )

Guess what, is just a python module which excepts a variable names urlpatterns.

Which means ...

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Topics : django rambling tips

Django aggregation tutorial

By : Shabda Raaj

One of the new and most awaited features with Django 1.1 was aggregation. As usual, Django comes with a very comprehensive documentation for this. Here, I have tried to put this in how-to form.

Jump to howtos or Get source on Github.

Essentially, aggregations are nothing but a way to perform an operation on group of rows. In databases, they are represented by operators as sum, avg etc.

To do these operations Django added two new methods to querysets.

  1. aggregate
  2. annotate

When you are have a queryset you can do two operations on it,

  1. Operate over the rowset to ...

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On Captcha

By : Shabda Raaj

When building public facing websites, spam is a real problem. Captcha has been teated as the first line of defence aginst this problem. If you must use captcha, here are some best practices working with them.

Can you do without one?

A lot of places captcha's are put to filter spam in user generated comment. One of the largest sources of UGC is comments on wordpress blogs. They do not use a captcha, and instead pass all comments through Akismet to verify which comments are spam, and reject the spams. In many cases, such a system would work for ...

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Topics : tips

Fun with none

By : rohit

(If you are in a hurry, here is the fun part.;) A few days ago, I was working with a nullable field, which wasn't behaving as I expected. So I started a shell, and see how nulls compare.

In [1]: None
In [2]: None > 10
Out[2]: False
In [3]: None < 10
Out[3]: True
In [4]: None == None
Out[4]: True
Funny, not as I expected. (Why is None < 10 True. I thought it would be either False or None or cause an Error?) So python is obviously broken, next steps, see the same thing in some other ...

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Django design patterns

By : Shabda Raaj

This is announcement about our new work, Django design patterns, a ebook about, well, Django design patterns. (Well imagine that!). Here is the readme copied from there.

[Edit] Syntax highlighting and indentation preservation were totally brroken. Fixed now.

Django design patterns is a book about commonly occuring patterns in Django. Not patterns in Gof sense, but patterns in the sense, we work this way, and it works for us. For us it is a ~pattern of work~ sense.

At this point this is just a lot of brain dump from us.

The latest sources are always available from http://github ...

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Topics : django tips book

Remote debugging - debugging pesky server only bugs

By : Shabda Raaj

Here is a quick tip. (Obvious if you work with Django for any length of time, but I have seen a few people who are not aware)

You can put debug trace import pdb; pdb.set_trace() in your code, and put it on the server. When you access this view from your local browser, the debug is still hit and you have a debug shell on your server where you can step through. (Obviously this works only if you ran the code via runserver. But runserver start the server to listen only on local connections. If ...

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Topics : django tips

Django Request Response processing

By : Shabda Raaj

Have you wondered the steps a users request goes through before being responded to by Django? The answer lies in reading django.core.handlers.base and django.core.handlers.wsgi. Here is a diagram explaining what happens. (Click to enlarge.)

The steps are. (With Apache/Mod_wsgi, similar steps for other setup.)

  1. User's request comes to Apache etc.
  2. Apache sends request to django.core.handlers.wsgi via mod_wsgi.
  3. A list of request and response middleware callables is created.
  4. Request middleware is applied. If it sends a response, it is returned to the user.
  5. urlresolvers.resolve finds the view funcion to ...

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Topics : django tips

Better Python package management using source and version control systems

By : lakshman

Thanks to awesome django community, there is plenty of open source django code around.

These packages get updated quite often and if you use it often like we do, you'd have possibly realized the need to manage these packages better.

Thankfully, all python ever needs is the source, and all you need to do is to place the source in the python path.

Most projects use Distributed Version Control Systems like Mercurial and Git, and they come locally with the entire history of the source which provides a lot of control to use any version of the code. For ...

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Understanding decorators

By : Shabda Raaj

If you used Django for any length of time, you would have come across the login_required decorator. You write @login_required before a view, and it magically becomes accessible only to authenticated users.

Decorators were introduced in python 2.4. PEP 318 is the PEP describing it. At the simplest decorators are nothing but callables returning other callables, and the decorator syntax @decorator is nothing but foo = bar(foo), where both bar and foo are callables.

Let us see some decorators in action.

In [1]: def good_function():
   ...:     print 'I am a good function'

In [2]: def decorator(orig_func):
   ...:     def bad_func():
   ...:         print ...

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Topics : python tips

Using Paypal with Django

By : Shabda Raaj

Paypal has a comprehensive API to use their services programatically. The ExpressCheckout API allows you to get the user's details and then process the payments on your servers. They include a SOAP and NVP API. With NVP you do a GET to the Paypal servers with Url encoded values, get responses in plain text and work with them.

The basic flow for ExpressCheckout is something like this,

  1. You make a SetExpressCheckout request to Paypal, passing your credentials and and the amount you want to charge etc.
  2. Paypal returns an response with ACK of SUCCESS and token which you need ...

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Topics : tips paypal

Building reusable Django apps

By : Shabda Raaj

Recently I updated a lot of our old apps to be compatible with Django 1.0 and be reusable. Before we go further, let me define a _ Reusable Django App _.

A Django app is reusable if

*  It is app. (That is, it is not a project, and has no
* It can be dropped in an existing project, and only places where the project should need editing are `` `installed_apps` and the projects level ``.
* It can be used in the project with an arbitrary url prefix.

The updated apps were written initially ...

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Topics : tips

Using subdomains with Django

By : Shabda Raaj

Django makes using beautiful urls a snap. However using subdomains with Django is not so obvious. Here is an article explaining this.

Advantages of subdomain

  1. Sometimes looks more professional. Users will prefer over
  2. If each part of your site is Under a different untrusted users, you might want to give them a separate subdomain, so that if they do Blackhat Seo on their part, the main site is not harmed.
  3. Your users can point a Cname to their subdomain to use domain of their choice with their subdomain.

Disadvantages of subdomain

  1. When you need ...

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Topics : tips

Dynamic forms with Django

By : Shabda Raaj

Newforms, (or forms now) are without doubt one of the coolest features of Django. (Of course after Admin, Localflavor, and many others). Here is some sample code.

class EmployeeForm(forms.Form):
    name = forms.CharField()
    age = forms.IntegerField()
    resume = forms.FileField()

Just this code gives you

  1. A form which knows how to render itself as Html.
  2. A form which knows how to validate data on the server side.
  3. A form which knows how to show the relevant errors.

However think of this scenario,

You need to customise your form depending on values in the Database.

What you want to do is ...

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Topics : tips forms

Generating PDFs with Django

By : Shabda Raaj

If your web app creates report chances are you also want this report in PDF form. The Django docs describe a way to generate PDFs using ReportLab. Here is some code from there.

from reportlab.pdfgen import canvas
from django.http import HttpResponse

def some_view(request):
    # Create the HttpResponse object with the appropriate PDF headers.
    response = HttpResponse(mimetype='application/pdf')
    response['Content-Disposition'] = 'attachment; filename=somefilename.pdf'

    # Create the PDF object, using the response object as its "file."
    p = canvas.Canvas(response)

    # Draw things on the PDF. Here's where the PDF generation happens.
    # See the ReportLab documentation for the full ...

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Topics : tips
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