Python Programming

Lesson 3

Web Applications

Create a new directory called web. Within it, create a new file called application.py

from flask import Flask

app = Flask(__name__)

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

To run it, open up a shell (double click StartVirtualEnvShell) and input the following:

set FLASK_APP=application.py
set FLASK_DEBUG=1
flask run

Let's break that down

from flask import Flask

app = Flask(__name__)

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

What is a route?

Looking at an example website: http://sensi-sl.org/

URL	Path
http://sensi-sl.org/	/
http://sensi-sl.org/events/	/events/
http://sensi-sl.org/about-us/	/about-us/
https://stats.sl/uploads/report.pdf	/uploads/report.pdf

Routes can support variables

@app.route("/hello/<name>")
def say_hello(name):
    if name is None:
        return "Hello World!"
    
    return "Hello %s" % name

Now, go to http://127.0.0.1:5000/hello/Sensi in your browser

Then, go to http://127.0.0.1:5000/hello/<yourname> in your browser.

Returning HTML

What you return gets displayed on the page.

You can serve raw HTML and it will render.

@app.route("/events/")
def events():
    return (
        "<ul>"
        "<li>Photoshop Training</li>"
        "<li>Python Training</li>"
        "<li>Word Training</li>"
        "<ul>"
    )

Returning HTML Files

You'll add the code to your .py file and create a folder called templates

/application.py
/templates
    /about-us.html

In about-us.html:

<h1>WHO WE ARE</h1>

<p>Sensi is building a technology innovation community in Sierra Leone ...</p>

from flask import render_template

@app.route("/about-us/")
def about_us():
    return render_template("about-us.html")

Once you've done that, go to http://127.0.0.1:5000/about-us/ in your browser.

Templates can support variables

Once you've done that, go to http://127.0.0.1:5000/about-us/ in your browser.

@app.route("/membership/")
def membership():
    plans = [
        {"name": "Student", "price": 50000},
        {"name": "Young Pro", "price": 70000}
    ]
    return render_template("membership.html", plans=plans)

In membership.html:

<h1>Membership Plans</h1>
<ul>
{% for plan in plans %}
    <li>{{plan.name}} costs Le {{plan.price}}</li>
{% endfor %}
</ul>

Once you've done that, go to http://127.0.0.1:5000/membership/ in your browser.