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"Web App" Exercise

Prerequisites

Learning Objectives

  • Create a basic web application in Python, using modular architecture.
  • Write routing logic to handle GET and POST requests, and respond by rendering HTML pages or returning JSON data.
  • Gain exposure to HTML templates, and using HTML forms to submit form data.
  • Run a web application in "development" using a local web server, and deploy to a user-facing "production" environment (i.e. a Heroku server).

References

Prompt

So, you've deployed a background web service to send you an email every day. But what if you wanted the information on-demand at the click of a button, without waiting for the next daily email? And what if you wanted to allow other people to register for your service? Let's build a web application interface into your application's functionality!

Instructions

Setup

To use the Flask package, let's first add Flask to the Daily Briefing repo's "requirements.txt" file, then re-install packages:

pip install -r requirements.txt

Guided Checkpoints

Now follow these sequential "checkpoints" for a guided walk-through of how to create a Flask application:

  1. Getting Started
  2. Routing
  3. Rendering HTML Pages
  4. Web Forms (and Handling POST Requests)

Stretch goals / further exploration:

  1. Twitter Bootstrap Styling (and Flash Messaging)
  2. Google Login - see this template repo and feel free to use it for your projects!!!

FYI: we'll be running the application using the following Flask command (not a Python command):

# Mac OS:
FLASK_APP=web_app flask run

# Windows OS:
# ... if `export` doesn't work for you, try `set` instead
export FLASK_APP=web_app
flask run

Deploying to Production

Reference:

After completing all the checkpoints and demonstrating the ability to successfully run the web app locally, let's re-deploy the source code:

git push heroku main

Heroku says "no web process specified". They want us to create a specific file called the "Procfile" in the repo's root directory to instruct the Heroku server which command to invoke in order to run the web app:

# this is the Procfile (a Heroku config file)

web: gunicorn "web_app:create_app()"

Since we're instructing the server to use the "gunicorn" package (Heroku's preferred tool) to run the web app on production, we'll also need to add gunicorn to the "requirements.txt" file so it will be installed on the server during the deployment process.

After saving the "Procfile" and "requirements.txt" files, make a commit before re-attempting to re-deploy:

git push heroku main

View the server logs and troubleshoot as necessary:

heroku logs --tail