Learning Python and Django

Print python module path


>>> import os
>>> print os.__file__
/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/os.pyc


>>> import django
>>> print django.__file__
/Library/Python/2.7/site-packages/django/__init__.pyc

Creating my first Django project
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1. django-admin.py startproject mysite


This creates the following structure:

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

These files are:

• The outer mysite/ 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. You can read all the details about manage.py in django-admin.py and manage.py.
• 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. import mysite.settings).
• mysite/__init__.py: An empty file that tells Python that this directory should be considered a Python package. (Read more about packages in the official Python docs if you're a Python beginner.)
• mysite/settings.py: Settings/configuration for this Django project. Django settings will tell you all about how settings work.
• mysite/urls.py: The URL declarations for this Django project; a "table of contents" of your Django-powered site. You can read more about URLs in URL dispatcher.
• mysite/wsgi.py: An entry-point for WSGI-compatible webservers to serve your project. See How to deploy with WSGI for more details.

The development server

Let's verify this worked. Change into the outer mysite directory, if you haven't already, and run the commandpython manage.py runserver. 

2. Creating an app for polls under this project

python manage.py startapp polls

That'll create a directory polls, which is laid out like this:

polls/
    __init__.py
    models.py
    tests.py
    views.py

This directory structure will house the poll application.

Edit the polls/models.py file.

But first we need to tell our project that the polls app is installed.

Edit the settings.py file again, and change the INSTALLED_APPS setting to include the string 'polls'. 

Now Django knows to include the polls app. Let's run another command:

python manage.py sql polls

The sql command doesn't actually run the SQL in your database - it just prints it to the screen so that you can see what SQL Django thinks is required. If you wanted to, you could copy and paste this SQL into your database prompt. However, as we will see shortly, Django provides an easier way of committing the SQL to the database.

If you're interested, also run the following commands:

• python manage.py validate -- Checks for any errors in the construction of your models.
• python manage.py sqlcustom polls -- Outputs any custom SQL statements (such as table modifications or constraints) that are defined for the application.
• python manage.py sqlclear polls -- Outputs the necessary DROP TABLE statements for this app, according to which tables already exist in your database (if any).
• python manage.py sqlindexes polls -- Outputs the CREATE INDEX statements for this app.
• python manage.py sqlall polls -- A combination of all the SQL from the sql, sqlcustom, and sqlindexes commands.

Looking at the output of those commands can help you understand what's actually happening under the hood.

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Questions:
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What are the common practices used by python based websites to improve performance ?