Simple Flask Application

Creating a simple URL Shortener Flask Application

• Technologies:
  • Python 3.9.7
  • pip 21.2.4
  • Basic HTML

MacOs/Linux	Windows
Terminal	Command Prompt
ls	dir
pwd	echo %cd%
export FLASK_APP=hello	set FLASK_APP=hello
path use /	path use /

Installing flask and pipenv

• change directory to flask_simple_url_shortener
• mac and linux users in terminal pip3 install pipenv
• windows users in gitbash or powershell pip install pipenv
• pipenv install to create pipfile.lock to hold all packages
• to enter virtual environment pipenv shell and to exit the virtual environment exit to go back to your terminal
• make sure you are in the virtual environment by again the command pipenv shell if you are already in the virtual environment then the console will print already activated. message
• to install flask on the virtual environment pipenv install flask
• ensure flask installed by simply running the command flask

Create first route in a flask app

• create hello.py and write some code
• to run the project in the virtual environment type for mac users export Flask_APP=hello / windows users set FLASK_APP=hello then flask run and that will run the server on http://127.0.0.1:5000/ or http://localhost:5000
• Note: if you change code in hello.py now then you should CTRL + C to exit the server then in terminal flask run so the server refreshes the content
• instead of stopping the server every time the code changes we could change the environment from production to development. Stop the server by hitting CTRL + C and type export FLASK_ENV=development and that will refresh the server automatically each time the code changes and file is saved.
• Note: opening a new terminal session means you must redefine FLASK_ENV=development and FLASK_APP=hello but we could save a step by just renaming the application to app.py and flask will recognize

Page templates in flask with Jinja

• create templates folder on same path of project, this folder will be looked up by flask to render html pages
• import render_template in app.py then specify render_template('HTML_FILE.html')
• to pass variables to jinja add variables as a argument after HTML file e.g. return render_template('HTML_FILE.html', name='jafer') in the function desired at app.py
• make a form with two fields for url and code(shortener) to the url using POST method