Writing your first Django app, part 1

Throughout this tutorial, we’ll walk you through the creation of a basic poll application.
It’ll consist of two parts:

• A public site that lets people view polls and vote in them.
• An admin site that lets you add, change, and delete polls.

You can tell Django is installed and which version by running the following command:

$ python -m django --version

Creating a project

You’ll need to auto-generate some code that establishes a Django project – a collection of settings for an instance of Django, including database configuration, Django-specific options and application-specific settings.

From the command line, cd into a directory where you’d like to store your code, then run the following command:

$ django-admin startproject mysite 

 

This will create a mysite directory in your current directory.

Let’s look at what startproject created:

mysite/
    manage.py
    mysite/
        __init__.py
        settings.py
        urls.py
        wsgi.py

These files are:

• The outer mysite/ root directory is just a container for your project. Its name doesn’t matter to Django; you can rename it to anything you like.  
• manage.py: A command-line utility that lets you interact with this Django project in various ways.
• The inner mysite/ directory is the actual Python package for your project. Its name is the Python package name you’ll need to use to import anything inside it (e.g. mysite.urls).
• mysite/__init__.py: An empty file that tells Python that this directory should be considered a Python package.
• mysite/settings.py: Settings/configuration for this Django project. 
• mysite/urls.py: The URL declarations for this Django project; a “table of contents” of your Django-powered site. URL dispatcher.
• mysite/wsgi.py: An entry-point for WSGI-compatible web servers to serve your project. 
• 
  

The development server

 Change into the outer mysite directory, if you haven’t already, and run the following commands:

$ python manage.py runserver 

    or 

$./manage.py runserver 

(Note : don't need to prefix python each time)

You’ve started the Django development server, a lightweight Web server written purely in Python.

Now that the server’s running, visit http://127.0.0.1:8000/ with your Web browser. 

 

You’ll see a “Welcome to Django” page, in pleasant, light-blue pastel. It worked!

 

 

Changing the port

By default, the runserver command starts the development server on the internal IP at port 8000.
 

localhost:8000

If you want to change the server’s port, pass it as a command-line argument. For instance, this command starts the server on port 8080:

$ python manage.py runserver 8080

If you want to change the server’s IP, pass it along with the port. So to listen on all public IPs (useful if you want to show off your work on other computers on your network), use:

$ python manage.py runserver 0.0.0.0:8000 

 

Automatic reloading of Server

The development server automatically reloads Python code for each request as needed. You don’t need to restart the server for code changes to take effect. However, some actions like adding files don’t trigger a restart, so you’ll have to restart the server in these cases.

Creating the Polls app :

Django comes with a utility that automatically generates the basic directory structure of an app, so you can focus on writing code rather than creating directories.

To create your app, make sure you’re in the same directory as manage.py and type this command:

$ python manage.py startapp polls 

or 

$ django-admin startapp polls

Projects vs. apps :

An app is a Web application that does something – e.g., a Weblog system, a database of public records or a simple poll app. 

A project is a collection of configuration and apps for a particular website.

 A project can contain multiple apps. An app can be in multiple projects.

This directory structure will house the poll application.

polls/
    __init__.py
    admin.py
    apps.py
    migrations/
        __init__.py
    models.py
    tests.py
    views.py

Write your first view :

Let’s write the first view. Open the file polls/views.py and put the following Python code in it:

polls/views.py

from django.http import HttpResponse 

def index(request):   

    return HttpResponse("Hello, world. You're at the polls index.")

To call the view, we need to map it to a URL - and for this we need a URLconf.

To create a URLconf in the polls directory, create a file called urls.py under polls app .

In the polls/urls.py file include the following code:

polls/urls.py

from django.conf.urls import url  

from . import views 

 urlpatterns = [ 

     url(r'^$', views.index, name='index'), 

]

 

The next step is to point the root URLconf at the polls.urls module. In mysite/urls.py, add an import for django.conf.urls.include and insert an include() in the urlpatterns list, so you have:

mysite/urls.py

from django.conf.urls import include, url  

from django.contrib import admin 

urlpatterns = [ 

     url(r'^polls/', include('polls.urls')), 

    url(r'^admin/', admin.site.urls), 

]

 

The include() function allows referencing other URLconfs. Note that the regular expressions for the include() function doesn’t have a $ (end-of-string match character) but rather a trailing slash. Whenever Django encounters include(), it chops off whatever part of the URL matched up to that point and sends the remaining string to the included URLconf for further processing.
 

The idea behind include() is to make it easy to plug-and-play URLs Since polls are in their own URLconf (polls/urls.py) .

 

When to use include() :




You should always use include() when you include other URL patterns. admin.site.urls is the only exception to this.

You have now wired an index view into the URLconf. Lets verify it’s working, run the following command:

$ python manage.py runserver

Go to http://localhost:8000/polls/ in your browser, and you should see the text “Hello, world. You’re at the polls index.”, which you defined in the index view.

 

The url() function is passed four arguments, two required: regex and view, and two optional: kwargs, and name.