title	subtitle	author
Dependecy checker in Python	adventures with asyncio	Johan Hidding

This is a literate program. The complete source code to this program is contained in the text of this document. You can view a web-friendly version at entangled.github.io/check-deps.

It struck me that, to get an Entangled/Bootstrap project to work, you need quite a few things installed. I wanted to have a script that checks all the dependencies and then reports back to the user. This script should follow these guidelines:

• require very little to run: It is beyond my Bash skills to implement this in pure Bash, so instead I settled on vanilla Python.
• be configurable: Python has a builtin parser for ini files.
• run efficiently: This is my chance to get my hands dirty with asyncio.

Configuration

The idea is to have a dependencies.ini file with entries that look as follows:

[python]
require = >=3.8
get_version = python3 --version
pattern = Python (.*)

The script will then run python3 --version and match the output to the regular expression Python (.*), from which a version number is extracted. This version is then compared to the requirement >=3.8.

Some version constraints may depend on other software to be present.

[pip]
require = >=19
get_version = pip --version
pattern = pip ([0-9.]*)
depends = python

If we have many Python packages to check for, it may be easier to do so through a template

[template:pip]
get_version = pip show {name} | grep "Version:"
pattern = Version: (.*)
suggestion_text = This is a Python package that can be installed through pip.
suggestion = pip install {name}
depends = python,pip

For instance, if we want to check the version of Numpy:

[numpy]
template = pip
require = >=1.0

When any dependency is missing, the script should print a friendly message informing the user how to proceed.