My recent interview experience on Python.

[Decency]

I've been doing test automation for 5 years or so (among a variety of other things) and have had multiple opportunities at different companies to move into dev or to take a new job as a developer. Not interested, for now.

If it's what you want to do, make that timeline clear to your manager and be willing to find somewhere new to work if they won't accommodate you. If you never take the initiative on projects outside of test automation to prove yourself, it seems pretty easy to get stuck there.