lect08, Thu 01/31

Flask

• Flask is a Python framework for building webapps.
• Python Web apps built with Flask can be deployed to the web at no cost via the free tier of Heroku.
• Bootstrap is a framework that allows you to quickly make websites that look professional

Today, we’ll dive into building sites with Flask and Bootstrap on Heroku.

Two Alternatives

• Dive into the deep end with this comprehensive tutorial: https://github.com/pallets/flask/tree/master/examples/tutorial/
• Go slow approach, going a little at a time through this: http://flask.pocoo.org/docs/1.0/quickstart/

Very Slow Approach

1. Create a github.com account and verify your email address
2. Create a heroku.com account and verify your email address
3. Create a repo called try_flask; the exact name is not important
4. Go into some folder where you do your work for this course.
5. Copy the URL from the green button for “Clone with HTTPS”
6. Type git clone followed by the URL that you copied
7. Create a new file on the website for your repo called hello.py
8. Paste into that file the contents from here: http://flask.pocoo.org/docs/1.0/quickstart/
9. Back at your command line, type git pull origin master and you should see the hello.py file come into your local directory.
10. Then, type this to define an environment variable FLASK_APP:

       export FLASK_APP=hello.py
    

On Windows Powershell, instead use:

   $env:FLASK_APP="hello.py"

1. Use this command to be sure flask is installed in your local Python:

      pip install flask
   

If you normally use pip3 instead, do that here:

   pip3 install flask

1. Use this command to start your server:

      flask run
   

Troubleshooting

If you get this warning:

* Environment: production
  WARNING: Do not use the development server in a production environment.
  Use a production WSGI server instead.

Here’s how to fix it:

export FLASK_ENV=development

Getting it running on Heroku

1. If you didn’t already, create an account at https://heroku.com and verify your email address.
2. Go to https://dashboard.heroku.com

3. Click “New”, then select “Create new app” to create a new heroku app. Give it a name such as chris-try-flask or try-flask-chris. The name has to be unique in all the world, so it’s helpful to put your own personal name into the name somehow. The name will eventually be your url, i.e. https://try-flask-chris.herokuapp.com

4. At the webpage of your github.com repo, click “Create new file” and make a new file called Procfile. It must be called exactly that, with exactly that sequence of upper and lowercase: capital P, lowercase rocfile.

   In the file, put this:

   web: gunicorn hello:app
   

5. Use this command to be sure gunicorn is installed in your local Python 3 system:

   pip install gunicorn
   

   If you normally use pip3 instead, do that here:

   pip3 install gunicorn
   

6. Create a new file called requirements.txt (exactly that spelling, and all lowercase).
   It should have the following in it.

   Flask
   gunicorn
   

7. Go back to the heroku dashboard, and select your app. For example, if you called your app phill-try-heroku, you should be able to click on phill-try-herokuand end up at this url:

   • https://dashboard.heroku.com/apps/phill-try-heroku

   From there, there should be an option to click where it says “Deploy”. Click on that.