Alpine frequent commands

Installing a package (let's show how to install python):

apk add python3 py3-pip

Specific version of a package (python or others).

• Go to Alpine Packages;
• Search for your specific version using filters (e.g. "python3");
• Open the package page with the right architecture;
• Look for the "version" field (which is composed by a number and a suffix; e.g. 3.8.6-r0);
• Launch this command:

apk add python3<3.8.6-r0
apk add py3-pip

It will install the last useful pip for your python version.

Using = and using < make no difference.

The procedure is equivalent for every Alpine package.

Other packages you may need

curl

apk add curl 

Rust

curl --proto '=https' --tlsv1.2 https://sh.rustup.rs -sSf | sh

Others in the comments.

--no-cache useful for Dockers

apk add --no-cache python3 py3-pip

Why?

It allows users to install packages with an index that is updated and used on-the-fly and not cached locally:

FROM gliderlabs/alpine:3.3

RUN apk --no-cache add nginx

EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

This avoids the need to use --update-cache and remove /var/cache/apk/* when done installing packages.