It should work to an extent on a mobile device, but I can't imagine how to make it a good user experience while actually coding. A tablet should be okayish, it's just not optimised for that. Typing code on a phone sounds awful.

For anyone who really wants that I recommend https://grasshopper.app/ to learn on the go while dragging and dropping, but this comes with serious limitations.

Ultimately I don't know what the long term plan is for someone without a desktop device. Do people write full programs on mobile devices? Is it easy enough to install external dependencies? To build and package software for release?

For sure. But I’ve heard of people who literally don’t have money for a computer and who so started coding on their phone.

https://news.ycombinator.com/item?id=27903630

It's impressive what some people can achieve under restraints.

Following the recommendation I started to use Pydroid (on Adroid) from the Playstore and even without an external keyboard it's great for little scripts (or exercises) on the go.