software installation - How do I figure out what package something is in without resorting to Google?

I often find myself wanting to install something, but I'm unsure of what package it's in. This is a very common occurrence for me:

$ make html
sphinx-build -b djangohtml -d _build/doctrees   . _build/html
make: sphinx-build: Command not found
make: *** [html] Error 127

$ sudo apt-get install sphinx

E: Unable to locate package sphinx

$ sudo apt-get install sphinx-build
E: Unable to locate package sphinx-build

googles

$ sudo apt-get install python-sphinx

Is there a better way?

Install apt-file and run apt-file update

Then use apt-file search sphinx-build to search for packages contanining a file named sphinx-build