This document provides an introduction and overview of Python and the Flask web framework. It discusses key Python concepts like objects, references, memory management and data types. It also covers Flask topics like routing, templates, request objects, sessions and authentication. The document aims to give readers a high-level understanding of Python and how to build basic web applications with Flask.

1. Python Master Class
Part 1
By Chathuranga Bandara
www.chathuranga.com

2. Today’s Agenda
Introduction to Python
Introduction to Flask

3. Python

4. What is Python… really..
Multi Purpose
Object Oriented
Interpreted?
Dynamically Typed and Strong as well
Readability and We are Adults!

5. Features
Cross Platform
Functional Support as well
Everything is an Object
Many Implementations
Batteries Included

6. Who Uses Python?

7. Why Python?

10. Versions
v2.7.X
v3.X

11. Some Tax…. i mean Syntax..

12. Indentation is the Key!

15. Types?

16. Not Strongly Typed
What the f*** that means?

17. Let’s Discuss Python Memory Management.

18. What is a C type Variable?

19. Variable location value
a 0x3FS 101
b 0x3F9 101
unique location These values live in a fixed
size bracket hence can only
hold same sized data or an
overflow happens

20. When we change one value
Variable location value
a 0x3FS 110
b 0x3F9 101
Data in the memory location
get overwritten

21. Python has Names not Variables

22. names
references
objects

23. Name is just a label for an object
In Python you can have multiple names for a single object

24. What is a reference?
Name or a container pointing to an object

25. ie:
110
x = 110
x
+1 reference count

26. 110
x = 110
y = 110
x
+2 reference count
y

27. Not sure?

28. also,
z = [110, 110]
110
x
y
Reference count: 4

29. Decrease Ref count?
110
x
reference count: 1
y
del will not delete the object but rather delete the reference to the object.

30. What happens when the ref count is 0?
Then it will delete the object. (what the garbage collector does in python)

31. Different types of objects then?
● Numbers
● Strings
● dict
● list
● classes

32. Because of names

34. Functions also can have names

35. Strings

36. Numbers

37. None is the new null

38. Lists

39. List Comprehension

40. Dictionaries

41. Mutable vs Immutable
Mutable : can alter
● list, dict, byte array, set
Immutable: otherwise
● Numbers, string, tuples, frozen sets

42. ie:
Is extremely inefficient

43. Much efficient

44. Control Flows - Conditionals

45. Loops

46. Functions

48. CLASSES

50. What is PIP?
pip is the Python package index

51. $ sudo apt-get install python-pip

52. Virtual Environment?

53. $ pip install virtualenv
$ cd my_project_folder
$ virtualenv name_of_the_virt
$ source name_of_the_virt/bin/activate
$ do pip sh*t
$ deactivate

54. Good practice!
Have a folder in root called requirements and inside that have following:
● dev.txt
● Prod.txt

55. Ie: dev.txt

56. $ pip install -r requirements/dev.txt

57. pip install Flask
# Import Flask library
from flask import Flask
# Initialize the app from Flask
app = Flask(__name__)
# Define a route to hello_world function
@app.route('/hello')
def hello_world():
return 'Hello World Again!'
# Run the app on http://localhost:8085
app.run(debug=True,port=8085)
python hello.py

60. Routing
@app.route('/')
def index():
return 'Index
Page'
@app.route('/hello')
def hello():
return 'Hello, World'

61. Variables?
@app.route('/user/<username>')
def show_user_profile(username):
# show the user profile for that user
return 'User %s' % username
@app.route('/post/<int:post_id>')
def show_post(post_id):
# show the post with the given id, the id is an integer
return 'Post %d' % post_id

62. That is sweet, what about the REST?

63. from flask import request
@app.route('/login', methods=['GET', 'POST'])
def login():
if request.method == 'POST':
do_the_login()
else:
show_the_login_form()

64. Rendering Templates
from flask import render_template
@app.route('/hello/')
@app.route('/hello/<name>')
def hello(name=None):
return render_template('hello.html', name=name)

65. Where the f**k is the template then?

66. <!doctype html>
<title>Hello from Flask</title>
{% if name %}
<h1>Hello {{ name }}!</h1>
{% else %}
<h1>Hello, World!</h1>
{% endif %}

67. Request Object
from flask import request
@app.route('/login', methods=['POST', 'GET'])
def login():
error = None
if request.method == 'POST':
if valid_login(request.form['username'],
request.form['password']):
return log_the_user_in(request.form['username'])
else:
error = 'Invalid username/password'
# the code below is executed if the request method
# was GET or the credentials were invalid
return render_template('login.html', error=error)

68. sessions

69. from flask import Flask, session, redirect, url_for, escape, request
app = Flask(__name__)
@app.route('/')
def index():
if 'username' in session:
return 'Logged in as %s' % escape(session['username'])
return 'You are not logged in'
@app.route('/login', methods=['GET', 'POST'])
def login():
if request.method == 'POST':
session['username'] = request.form['username']
return redirect(url_for('index'))
return ''' <form action="" method="post">
<p><input type=text name=username>
<p><input type=submit value=Login>
</form>
'''

70. @app.route('/logout')
def logout():
# remove the username from the session if it's there
session.pop('username', None)
return redirect(url_for('index'))
# set the secret key. keep this really secret:
app.secret_key = 'A0Zr98j/3yX R~XHH!jmN]LWX/,?RT'

71. That’s all for today Folks!