CF:G Python - Concepts

Recap

Programming in Python

Scripts, Modules & Packages

Functions & Expressions

Classes & Objects

Modules & Packages

The Python interpreter is the command line environment which allows us to run Python in the CLI, it interprets our Python code & produces the logical output

When you supply a file as input to the Python interpreter, it is called a script

Any Python file is a module

A collection of Python files/modules is a package

Details

Example:

from my_package import my_module_in_my_package

$ python my_script.py

Functions & Expressions

Functions take in arguments and apply an expression on it.

You can optionally return a value from a function to the runtime environment

# with argument & return
def add(a,b):
    return a+b

# without argument & return
def printHello():
    print "Hello!"

Classes & Objects

A class is a "blueprint" of an object, it defines properties & functions of a reusable piece of code which serves a specific purpose

An object is an instantiation of a class, a "live" version of the blueprint when it is initialised and run

Example:

# In file Song.py

class Song(object):

    def __init__(self, lyrics):
        self.lyrics = lyrics

    def sing_me_a_song(self):
        for line in self.lyrics:
            print line

# objects
happy_bday = Song(["Happy birthday to you",
                   "I don't want to get sued",
                   "So I'll stop right there"])

bulls_on_parade = Song(["They rally around tha family",
                        "With pockets full of shells"])

# run a function that the object is allowed to do
happy_bday.sing_me_a_song()

bulls_on_parade.sing_me_a_song()

So...

how do i work with data for dynamic websites and web applications?

Background...

And intro to HTTP & RESTful Web Services

THE HTML DOM

Document Object Model

Why is it useful to think of our HTML documents in this way?

But how can we transfer & manipulate data in our applications?

REST & HTTP

a standard way of handling, sending and responding to HTTP (Hyper-Text Transfer Protocol) requests. defines how applications are built to respond to requests for data

Standard request methods one can make to a RESTful API: GET - retrieve, POST - update, PUT - create, and DELETE - does what it says it will.

Applications built using REST allow clients to retrieve and manipulate data

Client application

Server application

database

PUT

POST

DELETE

GET

Flask

Jinja2
Requests

framework

templates

Python HTTP library

Fitting the pieces together

• HTTP & REST
  • Agreed way of sharing information over the Internet
• Requests
  • A Python library we can use to exchange small amounts of data with servers behind the scenes
• JSON
  • A way of representing data that is sent over the internet, which we will be using in this course

Requests

A library that someone has created for us to use the HTTP protocol easily

http://docs.python-requests.org/en/master/

JSON

Okay, so now we know roughly how we can programmatically fetch data (Requests), and how applications are built on the server-side to listen for our requests for data (REST architectures), how is the data received?

In this course, we will be receiving data that is sent back to us by servers as JSON - JavaScript Object Notation. JSON is a simple key-value mapping of data which is very quick to manipulate.

Example

For example, let’s use Facebook’s example which demonstrates how their Graph API is structured:

This GET request:

Returns this JSON:

{
    data:
    {
        is_silhouette: false,
        url: "https://scontent.xx.fbcdn.net/v/t1.0-1/p100x100/
            12006203_10154088276211729_2432197377106462187_n.png?oh=
            d1b6b18e1846c1adefd157a45c4d384d&oe=58226457"
    }
}

GET graph.facebook.com
 /facebook/picture?
   redirect=false

Facebook’s Graph API was built to handle requests with specific parameters, in order to return their logo to us in JSON format.

Postman

A good developer tool for testing HTTP requests

https://www.getpostman.com/