Flask

Flask: (web development, one drop at a time)

• microframework
• minimal features
• minimal code

Why Choose Flask:

• clean and simple: small app in a single python file
• un-opinionated: flexible, choose the components you need
• well-documented
• popular

Included with Flask:

• Jinja 2 - Templates
• Werkzeug - HTTP & routing
• Development Server and Debugger
• Unit testing support

Install Flask:

• python -m pip install flask

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flashcards.py
=========================================================
from flask import Flask, render_template, abort, jsonfy, request, redirect, url_for # app object represents as web app
from datetime import datetime
from model import db

app = Flask(__name__)   # flask constructor, creates: global flask application object,
                                         # name is special variable which is the python file name

@app.route('/')                 #decorator  called View Function
def welcome():
    return 'Welcome to flask'
    return render_template('welcome.html', msg='msg from view', name='boss', age=1000)
-------------------------------------------------------------------------------------
@app.route('/card')         #connecting database data
def card_view():
   card = db[0]
   return render_template('card.html', card=card)
-------------------------------------------------------------------------------------
@app.route('/card/<int:index>')      # parameter url 
def card_view(index):
   try:
      card = db[index]
      return render_template('card.html', card=card, index=index, max_index=len(db)-1)
   except IndexError:
      abort(404)
-------------------------------------------------------------------------------------
@app.route('/date')               
def date():
    return 'Page serverd at' + str(datetime.now())

#exercise: pages shows how many time it has visited
counter = 0
@app.route('/count_views')               
def count_views():
    global counter
    counter += 1
    return 'Page visited' + str(counter) + 'times'

/static
   /flasklogo.png
/templates    
   /welcome.html Notes:

• control flow is dictated by incoming HTTP Requests
• a view function is only called if its URL is requested (visited in browser)

=========================================================
Running Flask Application:    [NO SPACE at all]
=========================================================
# location of module containing our application, enable dev feature like debugging
export FLASK_APP=flashcards.py     #for windows, use 'set'
export FLASK_ENV=development    #for windows, use 'set'
flask run
python -m flask run                              # if app is not running by the previous line
                 # Ctrl + C  to stop the server
python    # see all app url, open terminal as python interpreter
import flashcards
flashcards.app.url_map

=========================================================
Jinja templates:
=========================================================

• displaying data to the user
• generating HTML
• calling templates from view
• passing data from view to template
• Jinja variables
• Templates: components that display data to the user
• Jinja templates generate text files: we use it to create HTML
• Templates are text files: with placeholders for variables, and logic: if/for/filters etc

Calling a template from a view:

• render_template: first arg is name of the template file. other arguments are data passed to the template context. and template should be in folder /tamplages

Jinja Variable:

• {{  msg }}
• Q {{  card.q }}.     Ans {{ card.a }}.    #card.html
• <button><a href="/card/{{ index+1 }}">NEXT</a></button>    # link of next card
• <a href="{{  url_for('card_view', index= index+1)  }}">NEXT</a>    best (viewName, params on view method)
• if template. [in view function:  max_index=len(db)-1]

{ % if  index<max_index %}

         <a href="{{  url_for('card_view', index= index+1)  }}">Next</a>

{ % else %}

        <a href="{{  url_for('card_view', index= 0)  }}">Start Over </a>

{ % endif %}

flashcards_db.json

[

  {"q":"name1", "ans":"10"},

  {"q":"name2", "ans":"20"}

]

• for template:   [in view function:  cards=db]

{% for card in cards %}
    <a href="{{ url_for('card_view', index=loop.index0) }}">{{  card.q  }}</a>
{% endfor  %}

=========================================================

Model:  

=========================================================

model.py

import json

def load_db():

    with open('flashcards_db.json') as f:

        return json.load(f)

def save_db():
    with open('flashcards_db.json', 'w') as f:
        return json.dump(db, f)

db = load_db()

Model-Template-View:

Serving REST API:

@app.route('/api/card')             
def api_card_list():
    return jsonfy(db)

@app.route('/api/card/<int:index>')             
def api_card_detail():
    try:
       return db[index]
   except IndexError:
      abort(404)


Add new card:
@app.route('/add_card', method=['GET','POST'])           
def add_card():
    if request.method == 'POST':
         card = {"question": request.form['question'], "answer": request.form['answer']}
         db.append(card)
         return redirect(url_for('card_view', index=len(db)-1))
    else:
         return render_tempalte('add_card.html')

add_card.html
<form method="post">
   <p>Question:<input type="text" name="question"></p>
   <p>Answer:<input type="text" name="answer"></p>
   <button type="submit"> Create </button>
</form>