Python has always had the ability to do callbacks (ie. first class functions), though admittedly it's not a common pattern and the stdlib doesn't support it for

Python has always had the ability to do callbacks (ie. first class functions), though admittedly it's not a common pattern and the stdlib doesn't support it for IO (also its anonymous function syntax is poor). There have been several libraries that provide the concept of a promise, but with modern python these are built into the stdlib with native async/await support, though many interfaces are still sync-only (though you can work around that with things like gevent that monkey-patch those interfaces to work with an event loop under the hood). I agree that python would be a poor fit for the kind of uses that JS in the browser usually serve, but it's really a matter of ecosystem, not core language design.