First do apk add py3-pip After that you have a basic python3 environment.
No need to separately install python3, since it is pulled in as a
dependency.
Rather than doing the usual pip install xxx which often fails on iSH
especially if the package needs to compile something, first try
apk search py3- | grep xxx
and if found do the matching apk add for that package.
If what you are looking for is available as an apk package it will work,
and it will install all dependencies.
So this is the prefered way to meet dependencies.
If you are lucky pip install xxx will work, but dont have too high
expectations...