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Python Sample App

This is a sample app to show how easy it is to get a Python application up and running.

Prerequisites

  • Python 3 is needed for this project. Python 2 is still installed by default on some sytems so you should ensure you have Python3 installed. Check like this:

    which python3

  • Pyenv will be used to manage the correct version. Pyenv is similar to rbenv and can be found here. To install on OS X:

    brew update
brew install pyenv

    This project was built using Python 3.9.1. We will install and manage this with pyenv:

    pyenv install 3.9.1

    This version is referenced in the .python-version file so it should be used automatically.

  • Poetry is used as a dependency and package manager. This tool will also manage our Python virtual environment to keep our dependencies contained. To install:

    curl -sSL https://raw.githubusercontent.com/python-poetry/poetry/master/get-poetry.py | python -

    This should add poetry to your PATH but if not, follow the instructions found in command line upon installation

Installation

Dependencies are specified within pyproject.toml file. To install, we use Poetry like this:

poetry install

This will install all dependencies into a virtual environment managed by Poetry. We can enter this environment and execute commands within like this:

poetry shell

Developing

This app is utilizing Flask, a popular micro-web framework built in Python.

The app is configured with environment variables found in the .env file and we can start the server after installation like this:

flask run

This will start the server at http://localhost:5000. If you navigate there, you should see the text "Hello World".

The code to do generate this view is in the hello module in hello.py.

This module defines a Flask blueprint at a root path

from flask import Blueprint


hello_bp = Blueprint('hello', __name__, url_prefix='/')

And then we use this blueprint to define our views:

@hello_bp.route('/')
def index() -> str:
  return "Hello World"

Blueprints are added to the main app in our root __init__.py.

Linting

We are using Flake8 as our code linting. It is installed with our main install as a dev dependency. To run it:

flake8

Linting errors look like the following:

./python_sample_app/hello.py:9:25: W292 no newline at end of file

Type Checking

Although Python is dynamically typed, it does support type hints, which is helpful for enforcing proper interfaces. The type checker mypy is installed as a dev dependency in Poetry. To run:

mypy python_sample_app/

This will report any issues like this:

python_sample_app/hello.py:9: error: Incompatible return value type (got "str", expected "int")

Testing

There are two libraries that we are using to assist with testing. The first is pytest. From the main project directory, we can run:

pytest

This will run all tests defined in the tests/ directory.

We can also analyze our code coverage using coverage:

coverage run -m pytest

This will run pytest and create a coverage report which can be viewed like:

coverage report