Flask

Intro to Python

already know the basics

Importing from other files

from functions import square

from the file functions.py you import the function 'square'

if __name__ == "_main_":
  main()

if currently running this particular file, run the 'main' function

Python Classes

class Point:
  def __init__(self, x, y):
    self.x = x
    self.y = y

Flask

Configuration

application.py

from flask import flask
app = Flask(__name__)
@app.route("/")
def index():
  return "Hello, world!"

To run the program and create a server:

go to directory of application.py
run $ flask run

Routing

from flask import flask
app = Flask(__name__)
@app.route("/")
def index():
  return "Hello, world!"
@app.route("/hrithik")
def hrithik():
  return "Hello, Hrithik!"

Smart Routing

from flask import flask
app = Flask(__name__)
@app.route("/")
def index():
  return "Hello, world!"
@app.route("/<string:name>")
def hello(name):
  return "Hello " + name + "!"

render_template

from flask import Flask, render_template
app = Flask(__name__)
@app.route("/")
def index():
  return render_template("index.html")

flask will only look for 'index.html' under a folder called templates

Passing variables

from flask import Flask, render_template
app = Flask(__name__)
@app.route("/")
def index():
  headline = "Hello"
  return render_template("index.html", headline = headline)

<!DOCTYPE html>
<html>
  <head>
    <title>My Website!</title>
  </head>
  <body>
    <h1>{{headline}}</h1>
  </body>
</html>

{{}} comes from Jinja2 syntax, a templating language used by Flask

If statements in HTML files

<!DOCTYPE html>
<html>
  <head>
    <title>My Website!</title>
  </head>
  <body>
    {% if new_year %}
      <h1>Yes! Happy new year</h1>
    {% else %}
      <h1>NO</h1>
  </body>
</html>

this is very similar to Ruby on Rails

for loops

<html>
  ...
    <ul>
      {% for name in names %}
      <li> {{ name }}</li>
      {% endfor %}
    </ul>
  ...
</html>

links for urls

<html>
  ...
    <a href="{{ url_for('index') }}"> index</a>
  ...
</html>

renders the page returned by the 'index' function

Template Inheritance

have a layout.html file in templates folder

<!DOCTYPE html>
<html>
  <head>
    <title>My Website!</title>
  </head>
  <body>
    <h1>{% block heading %}{% endblock %}</h1>
    {% block body %}
    {% endblock %}
  </body>
</html>

That block code tells the program that some html code could go between that.

Post Requests

{% extends "layout.html" %}
{% block heading %}
  First page
{% endblock %}
{% block body %}
  <form action ="{{url_for('hello')}}" method ="post">
    <input type="text" name="name" placeholder="Enter Your Name">
    <button> Submit</button>
  </form>
{% endblock %}

from flask import Flask, render_template, request
app = Flask(__name__)
@app.route("/")
def index():
  return render_template("index.html")
@app.rout("/hello", methods=["POST"])
def hello():
  name = request.form.get("name")
  return render_template("hello.html", name=name)

methods["POST"] makes it so that the method can only be called through POST Requests

Get Requests

from flask import Flask, render_template, request
app = Flask(__name__)
@app.route("/")
def index():
  return render_template("index.html")
@app.rout("/hello", methods=["GET", "POST"])
def hello():
  if request.method == "GET":
    return "Please submit form instead."
  else:
    name = request.form.get("name")
    return render_template("hello.html", name=name)

Sessions

from flask import Flask, render_template, request, session
from flask_session import Session
app = Flask (__name__)
app.config["SESSION_PERMANENT"] = False
app.config["SESSION_TYPE"] = "filesystem"
Session(app)
@app.route("/", methods=['GET', 'POST'])
def index():
  if session.get("notes") is None:
    session['notes'] = []
  if request.method == "POST":
    note = request.form.get("note")
    session['notes'].append(note)
  return render_template("index.html", notes=session['notes'])

Web Programming

SQL