Python Guild

2018.03.21

Web development with Flask

Flask is simple

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

And easy to setup

pip install flask

But it's also very flexible and modular

cat requirements.txt |grep flask

flask
flask-admin
flask-sqlalchemy
flask-restful
flask-wtf
flask-login
flask-hashing

Simplicity is easy to abuse

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"
    
@app.route("/user/login")
def login():
    return "Hello World!"
    
@app.route("/user/signup")
def signup():
    return "Hello World!"
    
    
@app.route("/video/upload")
def upload():
    return "ddd"
    
@app.route("/Whatever")
def upload():
    return "ddd"

This can turn ugly quickly. Use blueprints!

app.register_blueprint(home, url_prefix='/')
app.register_blueprint(user, url_prefix='/user')
app.register_blueprint(video, url_prefix='/video')

DB access?

SELECT * from ??

Rather not..

Use sqlalchemy!

user = db.session.query(models.Users).filter(models.Users.name == username).first()

Create table??

No.

Use Alembic for your migrations

ALCHEMY_URL=mysql+mysqlconnector://root:emarroot@localhost:3306/porghub APP_SECRET=mydevsecret alembic upgrade head                    
INFO  [alembic.runtime.migration] Context impl MySQLImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
INFO  [alembic.runtime.migration] Running upgrade  -> 86bba768a6c8, Added initial tables

Server?

python app.py?

Werkzeug is ok for development, but for prod we might need something more heavy.

UWSGI/GUNICORN

Static files?

Flask can serve static files, if you really want it, but why would you do that?

Use NGINX like you would normally

server{
   listen 80;
       location /static {
       root /usr/src;

       }
   location /{
      include uwsgi_params;
      uwsgi_pass uwsgi:3031;

      proxy_redirect     off;
        proxy_set_header   Host $host;
        proxy_set_header   X-Real-IP $remote_addr;
        proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header   X-Forwarded-Host $server_name;
   }

}

With time you'll need an admin interface

Why code, when you dont have to?

flask-admin

admin.add_view(MyModelView(models.Users, db.session,
                        column_list=['id', 'name', "description", "is_active", "is_admin"],
                        search_fields=['username'],
                        form_columns=['id', 'name', "description", "is_active", "is_admin"]))

Sessions?

session['userid'] = 'ugly'

use flask-login

user = db.session.query(models.Users).filter(models.Users.name == username).first()

if not user or user and not hashing.check_value(user.password, password, settings.SECRET):
    flash("Failed to log you in with these credentials")
    return render_template("login.html", form=form)

else:
    #login
    login_user(user)
    return redirect('//')

Forms, and views

Flask-wtf

Jinja2

Template inheritance

Validations

Fun

login.html

{% extends "base.html" %}

{% block container %}

<body>
   <div class = "container">
      <h4>Register</h4>
      <br>
      {% from "_formhelpers.html" import render_field %}
      <form method=post action="/user/login">
         <dl>
            {{render_field(form.username)}}
            {{render_field(form.password)}}
                <input name=_csrf_token type=hidden value="{{ csrf_token() }}">

         </dl>
         <p><input type=submit value=Login></p>
      </form>

      {% if error %}
         <p class="error"><strong>Error:</strong>{{error}}</p>
      {% endif %}

   </div>
</body>

{% endblock %}

login form


class LoginForm(Form):
    username = StringField('Username', [validators.DataRequired()])
    password = PasswordField('Password', [validators.DataRequired()])