Python was created by Guido van Rossum in the late 1980s and named after Monty Python. It is a general purpose, high-level programming language that supports multiple paradigms like object-oriented, functional, and imperative programming. Django is a Python web framework that grew out of a newspaper project and follows the MVC pattern, separating concerns into models, views, templates. It provides tools for authentication, forms, administration, and more so that developers can focus on their specific applications.

1. Introduction to
(Python and)
the Django Framework
Prashant Punjabi
Solution Street
9/26/2014

2. Python
!
• Created by Guido van Rossum
in the late 1980s
!
• Named after ‘Monty Python’s
Flying Circus’
!
• Python 2.0 was released on 16
October 2000
!
• Python 3.0 a major,
backwards-incompatible
release, was released on 3
December 2008
!
• Guido is the BDFL

3. Python
• General Purpose, high-level programming language
• Supports multiple programming paradigms
• object-oriented, functional, structured, imperative(?)
• Dynamically typed
• Many implementations
• CPython (reference)
• Jython
• IronPython .. and many more

4. The Zen of Python
• “Core philosophy”
• Beautiful is better than ugly
• Explicit is better than implicit
• Simple is better than complex
• Complex is better than complicated
• Readability counts
• >>> import this

5. Data Types
• Numbers
• int, float, long (and complex)
• Strings
• str, unicode
• Sequence Types
• str, unicode, lists, tuples (and bytearrays, buffers, xrange)
• strings, tuples are ‘immutable’
• lists are mutable
• Mapping Types
• dict

6. Functions
• Defined using the keyword.. def
• Followed by the function name and the parenthesized list of formal parameters.
• The statements that form the body of the function start at the next line,
• and must be indented (just like this line)
• The first statement of the function body can optionally be a string literal
• this string literal is the function’s documentation string, or docstring.
• Arguments are passed using call by value (where the value is always an object
reference, not the value of the object)
• Functions always return a value
• If not return is explicitly defined, the function returns None

7. Control Flow
• if
• if…elif…else
• for
• range
• break, continue, else
• while

8. Truthi-nessTM
• An empty list ([])
• An empty tuple (())
• An empty dictionary ({})
• An empty string ('')
• Zero (0)
• The special object None
• The object False (obviously)
• Custom objects that define their own Boolean context behavior (this is
advanced Python usage)

9. Modules and Packages
• A module is a file containing Python definitions and statements.
• The file name is the module name with the suffix .py appended.
• Within a module, the module’s name (as a string) is available as the value of the
global variable __name__
• Modules can be executed as a script
• python module.py [args]
• __name__ is set to __main__
• Packages are a way of structuring Python’s module namespace by using “dotted
module names”
• The __init__.py file is required to make Python treat a directory as containing
packages

10. Classes
• Python’s class mechanism adds classes with a minimum of new syntax and
semantics
• Python classes provide all the standard features of Object Oriented
Programming
• multiple base classes
• a derived class can override any methods of its base class or classes
• a method can call the method of a base class with the same name
• Objects can contain arbitrary amounts and kinds of data
• Class and Instance Variables
• Static Methods

11. Standard Library
• Operating System Interface
• File handling
• String pattern matching
• Regular expressions
• Mathematics
• Internet Access
• Dates and Times
• Collections
• Unit Tests

12. Batteries Included

13. Django

14. Django
• Django grew organically from real-world applications
• Born in the fall of 2003, in Lawrence, Kansas, USA
• Adrian Holovaty and Simon Willison - web
programmers at the Lawrence Journal-World
newspaper
• Released it in July 2005 and named it Django, after the
jazz guitarist Django Reinhard
• “For Perfectionists with Deadlines”

15. Getting Started
• Installation
• pip install Django
• ¯_(ツ)_/¯
• Creating a Django project
• django-admin.py startproject django_example
• Adding an ‘app’ to your Django project
• python manage.py startapp music

16. MVC - Separation of Concerns
• models.py
• description of the database table, represented by a Python class, called a model
• create, retrieve, update and delete records in your database using simple Python code
• views.py
• contains the business logic for the page
• contains functions, each of which are called a view functions or simply views
• urls.py
• file specifies which view is called for a given URL pattern
• Templates
• describes the design of the page
• uses a template language with basic logic statements

17. models.py
• Each model is represented by a class that subclasses django.db.models.Model
• Class variables represents a database fields in the model
• A field is represented by an instance of a Field class eg CharField,
DateTimeField
• The name of each Field instance is used by the database as the column name
• Some Field classes have required arguments, others have optional arguments
• CharField, for example, requires that you give it a max_length
• default is an optional argument for many Field classes
• ForeignKey field is used to define relationships
• Django supports many-to-one, many-to-many and one-to-one

18. Queries
• Each model has at least one Manager, and it’s called objects by default.
• Managers are accessible only via model classes
• Enforce a separation between “table-level” operations and “record-
level” operations.
• A QuerySet represents a collection of objects from your database
• It can have zero, one or many filters
• A QuerySet equates to a SELECT statement, and a filter is a limiting
clause such as WHERE or LIMIT.
• Example

19. Migrations
• New in Django 1.7
• Previously accomplished by an external package called south
• Keeps the database in sync with the model objects
• Commands
• migrate
• makemigrations
• sqlmigrate
• squashmigrations
• Data Migrations
• python manage.py makemigrations --empty music

20. urls.py
• Django lets you design URLs however you want, with no
framework limitations.
• “Cool URIs don’t change”
• URL configuration module (URLconf)
• simple mapping between URL patterns (regular expressions)
to Python functions (views)
• capture parts of URL as parameters to view function (named
groups)
• can be constructed dynamically

21. views.py
• A Python function that takes a Web request and returns a Web response
• HTML contents of a Web page,
• a redirect, or a 404 error,
• an XML document,
• an image
• . . . or anything
• The convention is to put views in a file called views.py
• but it can be pretty much anywhere on your python path
• ‘Django Shortcuts’
• redirect, reverse, render_to_response,

22. Templates
• Designed to strike a balance between power and ease
• A template is simply a text file. It can generate any text-based format (HTML, XML,
CSV, etc.).
• Variables - {{ variable }}
• Replaced with values when the template is evaluated
• Use a dot (.) to access attributes of a variable
• Dictionary lookup, attribute or method lookup or numeric index lookup
• {{ person.name }} or {{ person.get_full_name }} or {{ books.
1 }}
• Filters can be used to modify variables for display
• {{ name|lower }}

23. Templates
• Tags control the logic of the template
• {% tag %}
• Commonly used tags
• for
• if, elif and else
• block and extends - Template inheritance

24. Template Inheritance
• Most powerful part of Django’s template engine
• Build a base “skeleton” template that contains all the
common elements of your site and defines blocks that
child templates can override.
• {% extends %} must be the first template tag in that
template.
• More {% block %} tags in your base templates are
better
• Child templates don’t have to define all parent blocks

25. Forms
• Django handles three distinct parts of the work involved in forms
• preparing and restructuring data ready for rendering
• creating HTML forms for the data
• receiving and processing submitted forms and data from the client
• The Django Form class
• Form class’ fields map to HTML form <input> elements
• Fields manage form data and perform validation when a form is submitted
• Fields are represented to a user in the browser as HTML “widgets”
• Each field type has an appropriate default Widget class, but these can be
overridden as required.

26. Batteries (still) included
• Authentication and Authorization
• Emails
• File Uploads
• Session
• Caching
• Transactions
• .. and so on

27. See also..
• The Django ‘admin’ app
• django-admin.py and manage.py
• ModelForms
• Generic Views or Class based views
• Static File deployment
• Settings
• Middleware
• Similar to Servlet Filters in Java

28. References
• Python - Wikipedia page (http://en.wikipedia.org/wiki/
Python_(programming_language))
• The Python Tutorial (https://docs.python.org/2/tutorial/
index.html)
• The Django Project (https://www.djangoproject.com/)
• The Django Book (http://www.djangobook.com/en/2.0/
index.html)
• The Django Documentation (https://
docs.djangoproject.com/en/1.7/)

29. Questions?

30. Thank you!