pynix

Welcome to pynix! This is a small project aimed at learning python programming. It focuses on the implementation of a command line program that implements some familiar Linux commands. The goal is to learn a about the python ecosystem -- some important libraries, idioms and patterns that frequently appear in the context of python programming projects.

Initial setup

1. Clone this git repository
2. Create a branch to work in git switch -c <branchname>
3. Create a new virtual environment for your project.
4. Install the requirements (venv) cd pynix && python -m pip install -r requirements.txt
5. Install pynix in development mode (venv) python -m pip install -e .

Once you've got this done, you should be able to run pynix:

(venv) pynix 
Hello from pynix!

The program currently has one specifically defined entrypoint pynix that functions more or less like an alias to call the main routine of the program, which is found in the src/cli.py module.

Tasks

The initial tasks focus on implementing a command line program from which it is possible to run simplified versions of the well-known Unix programs cat and less. Read up on the argparse library and figure out the steps needed in order to implement the functionality described below.

Readings

• PEP 8 Style Guide for Python Code
• Chapters 3 & 4, Programming Python by Mark Lutz
• Manual pages for cat and less
• Python docs for: argparse, os, sys, pathlib
• Chapters 1, 2, 5, 6, Serious Python by Julien Danjou

Implement cat

The Linux man page for cat states that it is a program to "concatenate files and print on the standard output". In order to replicate this functionality your program will need to be able to read a variable number of arguments from stdin. It should check that each of these arguments can be converted to a valid pathlike object and then it should open and read the file, writing its contents to stdout.

The usage for the cat command would be as follows:

pynix --cat <file1> [<file2> <file3> ... <fileN>]

Implement tail

Tail is another small utility program which comes from Unix. When called, it outputs the last part of files passed as arguments. In this implementation, we want to target the ability to specify how long the tail should be (how many lines) and the file which should be read and printed to stdout.

pynix --tail <length (int)> <file>

Implement some helpful error messages

If the program receives the wrong number of arguments as input, it should be able to fail gracefully with a helpful error message for the user. This tends to be handled by printing a usage statement to stdout for the user.

pynix --cat 
usage: pynix --cat <file1> [<file2> <file3>]

Change the name of the command line program

Personalize the program so that it's possible to call it with another name. For example, you could abbreviate the name to pyx in order to lessen the amount of typing that you have to do at the command prompt in order to run the program. The purpose of this exercise is to think a little bit about how the python project is structured. Historically, the python ecosystem for

Implement some tests to show that your program behaves as expected

Basically we want to use this opportunity to introduce pytest a very useful testing library. You can focus on implementing two types of tests specifically: unit tests and integration tests. You might have to do a little bit of research to figure out what the different types do.

You can invoke pytest by running:

pytest tests/tests.py