I have dont android development from quite some time, developed few projects. I want to increase my knowledge, pleade recommend me some advance books on android Thanks! PS : I am not so confident in Broadcast Receivers and Services

I am confused which should I learn, Django/Python or NodeJS/ExpressJS. I am new to both of them. I am trying to create a back end for my android application but can't decide which language to choose.

I am confused which should I learn, Python/Django or Node.js/Express.