python master class part 1
TRANSCRIPT
Python Master ClassPart 1
By Chathuranga Bandarawww.chathuranga.com
Today’s Agenda
Introduction to Python
Introduction to Flask
Python
What is Python… really..
Multi Purpose
Object Oriented
Interpreted?
Dynamically Typed and Strong as well
Readability and We are Adults!
Features
Cross Platform
Functional Support as well
Everything is an Object
Many Implementations
Batteries Included
Who Uses Python?
Why Python?
Versions
v2.7.X
v3.X
Some Tax…. i mean Syntax..
Indentation is the Key!
Types?
Not Strongly TypedWhat the f*** that means?
Let’s Discuss Python Memory Management.
What is a C type Variable?
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
When we change one value
Variable location value
a 0x3FS 110
b 0x3F9 101
Data in the memory location get overwritten
Python has Names not Variables
names
references
objects
Name is just a label for an objectIn Python you can have multiple names for a single object
What is a reference?Name or a container pointing to an object
ie:
110
x = 110
x
+1 reference count
110
x = 110y = 110
x
+2 reference count
y
Not sure?
also,
z = [110, 110]
110
x yReference count: 4
Decrease Ref count?
110
x
reference count: 1
y
del will not delete the object but rather delete the reference to the object.
What happens when the ref count is 0?Then it will delete the object. (what the garbage collector does in python)
Different types of objects then?● Numbers● Strings
● dict● list● classes
Because of names
Functions also can have names
Strings
Numbers
None is the new null
Lists
List Comprehension
Dictionaries
Mutable vs Immutable Mutable : can alter
● list, dict, byte array, set
Immutable: otherwise
● Numbers, string, tuples, frozen sets
ie:
Is extremely inefficient
Much efficient
Control Flows - Conditionals
Loops
Functions
CLASSES
What is PIP?pip is the Python package index
$ sudo apt-get install python-pip
Virtual Environment?
$ pip install virtualenv$ cd my_project_folder$ virtualenv name_of_the_virt$ source name_of_the_virt/bin/activate
$ do pip sh*t
$ deactivate
Good practice!Have a folder in root called requirements and inside that have following:
● dev.txt● Prod.txt
Ie: dev.txt
$ pip install -r requirements/dev.txt
pip install Flask
# Import Flask libraryfrom flask import Flask # Initialize the app from Flaskapp = Flask(__name__) # Define a route to hello_world [email protected]('/hello')def hello_world(): return 'Hello World Again!' # Run the app on http://localhost:8085app.run(debug=True,port=8085)
python hello.py
Routing
@app.route('/')
def index():
return 'Index
Page'
@app.route('/hello')
def hello():
return 'Hello, World'
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
That is sweet, what about the REST?
from flask import request
@app.route('/login', methods=['GET', 'POST'])
def login():
if request.method == 'POST':
do_the_login()
else:
show_the_login_form()
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)
Where the f**k is the template then?
<!doctype html>
<title>Hello from Flask</title>
{% if name %}
<h1>Hello {{ name }}!</h1>
{% else %}
<h1>Hello, World!</h1>
{% endif %}
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)
sessions
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>
'''
@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'
That’s all for today Folks!