There are a couple of search engines that do this. Sometimes when I get stuck on a underdocumented Python library, the big G will take me to one via a search on a method or constant. I can then see the code from other open source libraries/projects.

I don’t have any links saved, since they feel kinda sketch (ads all over the place). But it has been very helpful, unlike searching within GitHub for a string that I know is in the repo.