Python Flask

Table of Contents

• Python Flask
  • Table of Contents
  • Development machine
    • Mac version
      • Install Python3 and dependencies
    • Install Docker
    • Windows version
      • Install Python3
      • Install dependencies
    • Useful commands
    • Other tools
    • Testing
  • Resources

Development machine

Windows and Apple devices have different configuration. For an Apple device, Python 3 is known as python3, therefore pip is also known as pip3.

Mac version

To install Python 3 and its dependencies, we will use Homebrew. You can install Homebrew from here.

Install Python3 and dependencies

brew install python3

To check if it was installed, just run python3 --version.

Install virtualenv: pip3 install virtualenv.

Go to esrs-backend and start venv: virtualenv venv

After installing the virtualenv, then you need to activate it: source venv/bin/activate.

Install dependencies from dev-requirements.txt: pip3 install -r requirements/dev-requirements.txt.

Install all git hooks locally by running python3 -m python_githooks.

Tell Flask where is the entry point: export FLASK_APP=app.py. Required only if the app is used the default web server and then started with flask run.

Start the application: gunicorn app:app.

Et voila, you have a working Flask application.

Once finished with the virtual environment, you need to deactivate it: deactivate.

Install Docker

Follow the installation steps described on the official website. Minimum version for Docker for Mac is Docker version 19.03.5, build 633a0ea.

Windows version

This has been tested on python 3.8.0. If you have problems installing, check you are on this version.

Install Python3

• Python can be downloaded and installed from this link

Install dependencies

• Download docker from here
  • Leave UNIX file system on if asked.
• In ./scripts, run win_docker.bat
• This should install the docker image and start the server.
  • If it fails, try removing the -d flag from the second command to run the server in the foreground.

Useful commands

• Freeze dependencies and create requirements.txt: pip3 freeze >requirements.txt;
• Install dependencies from requirements.txt: pip install -r requirements.txt;
• Build a Docker image locally (you need to be in the root directory of the project): docker build -t backend:latest ..
• List all local Docker images: docker images. This should list your newly created image.
• Run locally your new image: docker run --name backend -d -p 8000:5000 --rm backend:latest. Now you can access the app at http://localhost:8000/.
• Run all tests: coverage run -m unittest or python -m unittest.
• View test coverage after running with coverage: coverage report.
• Run the application with one command: FLASK_APP=app.py flask run or to use gunicorn gunicorn app:app.
  • gunicorn is MAC only. For development on Windows, the normal Flask environment is fine.
• Run linter: flake8 app.

Other tools

• For linting and style guide enforcement we use flake8. You can run it with flake8 app. Configuration file is .flake8.
• For git hooks, we use python-githooks. It has hooks defined in .githooks.ini. After updating a hook , you need to run python -m python_githooks in order to add new hooks.
  • Windows users - this must be executed in a bash environment, either through git bash or Windows' Linux subsystem.
• For code coverage we use Coverage. It works based on .coveragerc config file.
• Green Unicorn as our production web server.

Testing

For tests we use unittest. As a convention, it picks up all test files that are in directory test/ and name starts with test_.

Resources

• Learning Flask
• Flask mega-tutorial