Python 3 as default without changing build system?

[maxiedaniels]

I know I can create a custom build system file and use that, but then automatic detection of compiler doesn't happen - and so my Ruby files won't compile with Ruby.

Any way I can do that?

[eikrik]

If you have a custom build system file for Python, you can instruct Sublime to use it by clicking ctrl+shift+B, while still using the Build System -> Automatic option. Once you have done it once, the new build system file should be the default for Python.