Flask Introduction - Python Meetup
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Flask is a micro web development framework for Python that keeps its core simple but allows for extensibility. It emphasizes building applications with extensions rather than having all functionality contained within the framework. A minimal Flask app requires only a few lines of code and runs a development server. Templates can be rendered to generate dynamic HTML content by passing context through the render_template function. Flask supports common features like request handling, cookies, sessions, and file uploads through extensions.
![HTTP Method
By default, a route only answers GET requests, but this can be changed by
providing the methods argument to the route() decorator:
@app.route('/login', methods=['GET', 'POST'])
def login():
if request.method == 'POST':
do_the_login()
else:
show_the_login_form()
We can ask Flask do the hard work and use decorator:
@app.route ( ’/login ’ , methods =[ ’ GET ’ ])
def show_the_login_form ():
...
@app.route ( ’/login’ , methods =[ ’ POST ’ ])
def do_the_login ():
...](https://image.slidesharecdn.com/flaskintroduction-pythonmeetup21march2013-130321074231-phpapp01/85/Flask-Introduction-Python-Meetup-7-320.jpg)
![Rendering templates
To render a template you can use the render_template() method:
from flask import render_template
@app.route('/hello/')
@app.route('/hello/<name>')
def hello(name=None):
return render_template('hello.html', name=name)
Let's say you want to display a list of blog posts, you will connect to your DB and
push the “posts” list to your template engine:
@app.route('/posts/')
def show_post():
cur = g.db.execute('SELECT title, text FROM post')
posts = [dict(title=row[0], text=row[1]) for row in cur.fetchall()]
return render_template('show_post.html', posts=posts)](https://image.slidesharecdn.com/flaskintroduction-pythonmeetup21march2013-130321074231-phpapp01/85/Flask-Introduction-Python-Meetup-8-320.jpg)
Flask Introduction - Python Meetup
- 1. Flask, for people who like to have a little drink at night Areski Belaid <[email protected]> 21th March 2013 slideshare.net/areski/
- 2. Flask Introduction What is Flask? Flask is a micro web development framework for Python What is MicroFramework? Keep the core simple but extensible “Micro” does not mean that your whole web application has to fit into one Python file
- 3. Installation Dependencies: Werkzeug and Jinja2 $ sudo pip install virtualenv $ virtualenv venv $ . venv/bin/activate $ pip install Flask If you want to work with databases you will need: $ pip install Flask-SQLAlchemy
- 4. QuickStart A minimal Flask application looks something like this: 1. from flask import Flask 2. app = Flask(__name__) 3. @app.route('/') 4. def hello_world(): return 'Hello World!' 5. if __name__ == '__main__': app.debug = True app.run() Save and run it with your Python interpreter: $ python hello.py * Running on http://127.0.0.1:5000/
- 5. This is the end... You can now write a Flask application!
- 6. URLs The route() decorator is used to bind a function to a URL: @app.route('/') def index(): return 'Index Page' @app.route('/hello') def hello(): return 'Hello World' We can add variable parts: @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): return 'Post %d' % post_id
- 7. HTTP Method By default, a route only answers GET requests, but this can be changed by providing the methods argument to the route() decorator: @app.route('/login', methods=['GET', 'POST']) def login(): if request.method == 'POST': do_the_login() else: show_the_login_form() We can ask Flask do the hard work and use decorator: @app.route ( ’/login ’ , methods =[ ’ GET ’ ]) def show_the_login_form (): ... @app.route ( ’/login’ , methods =[ ’ POST ’ ]) def do_the_login (): ...
- 8. Rendering templates To render a template you can use the render_template() method: from flask import render_template @app.route('/hello/') @app.route('/hello/<name>') def hello(name=None): return render_template('hello.html', name=name) Let's say you want to display a list of blog posts, you will connect to your DB and push the “posts” list to your template engine: @app.route('/posts/') def show_post(): cur = g.db.execute('SELECT title, text FROM post') posts = [dict(title=row[0], text=row[1]) for row in cur.fetchall()] return render_template('show_post.html', posts=posts)
- 9. Rendering templates (next) The show_posts.html template file would look like: <!doctype html> <title>Blog with Flask</title> <div> <h1>List posts</h1> <ul> {% for post in posts %} <li><h2>{{ post.title }}</h2>{{ post.text|safe }} {% else %} <li><em>Unbelievable, there is no post!</em> {% endfor %} </div>
- 10. More and more and more... ○ Access request data ○ Cookies ○ Session ○ File Upload ○ Cache ○ Class Base View ○ … Flask has incredible documentation...
- 11. Flask vs Django Flask Django Template Jinja2 Own Signals Blinker Own i18N Babel Own ORM Any Own Admin Flask-Admin Builtin-Own * Django is large and monolithic Difficult to change / steep learning curve * Flask is Small and extensible Add complexity as necessary / learn as you go
- 12. Lots of extensions http://flask.pocoo.org/extensions/ ● YamlConfig ● WTForm ● MongoDB flask ● S3 ● Resful API ● Admin ● Bcrypt ● Celery ● DebugToolbar
- 13. Admin https://pypi.python.org/pypi/Flask-Admin Very simple example, how to use Flask/SQLalchemy and create an admin https://github.com/MrJoes/Flask-Admin/tree/master/examples/sqla
- 14. Conclusion - Flask is a strong and flexible web framework - Still micro, but not in terms of features - You can and should build Web applications with Flask
- 15. Hope you enjoyed it! Questions? slideshare.net/areski/ github.com/areski/ twitter.com/areskib Contact email : [email protected]