Python Katas

This repository provides some simple code katas in Python and an instruction on how to set up a Python project with a testing environment on your local (mac).

Usage

Install Python

Location agnostic type

$ brew install python3

Use Python in the command line

$ python3 
>>> import this
(find joy in reading the Zen of Python)
>>> quit()

Or play with Python on Jupyter Notebook preferably on your local

$ pip3 install notebook
$ jupyter notebook

Then in your browser on http://localhost:8888/ go to New -> Python3 and start coding without tests :)

Install a virtual environment

Install the virtualenv

$ pip3 install virtualenv

In your project directory, create the virtual environment (that is a directory venv where all libraries of your project live)

$ virtualenv -p python3 venv

Activate the virtual env

$ . venv/bin/activate

Install packages on your project

In your root directory, create a file requirements.txt and add your favourite packages to it. For now those will be:

• pytest: unit test framework
• pyhamcrest: matcher objects in assert statements
• flake8: syntax checks / linter
• mypy: type annotation checks

Install the packages with

$ pip install -r requirements.txt

By running this command the above packages will be installed only on your project. In this way you can provide different versions per project.

Add the created venv directory to your .gitignore. Developers who will work on your project will pull the requirements.txt from your repository and install all required packages with the above command.

Notes on usage

Flake8

When opening your project in VSCode for the first time, your IDE will ask you to install a linter. Click Select Linter and chose Flake8.

Mypy

mypy validates types and can be pretty annoying sometimes. You can disable it with # type: ignore where ever needed (see example). But in general, type checks make sense of course. Out of the box, mypy validates simple types such as int, str, float, bool. To validate more complex types (list, tuple, dict, ..) we have to import the types from the built-in library in the code, e.g. from typing import Tuple.

How to test

Run the test suites in your root directory

$ venv/bin/pytest -vvv
$ venv/bin/pytest binary_search/test_binary_search.py -vvv

Pytest will show print output from your code in the command line only on test failure. You can disable per-test capturing with -s

$ venv/bin/pytest -s

Fixtures

Store your fixture file as /tests/fixtures/fixture.txt. In your test_example.py use Pytest's fixture decorator to create a method that reads the file and returns its content. Pass this method as an argument into your test method.

Use the following code to provide fixtures in your test:

import pytest

@pytest.fixture
def fixture_content():
    with open("tests/fixtures/fixture.txt") as f:
        return f.read()
        
def test_runs_example(fixture_content):
    expected = "expected output"
    actual = run(fixture_content)
    assert_that(actual, equal_to(expected))

Using Python's Content Manager (with statement) will open the fixture file, read from it and then close it.