Astropy Proposal for Enhancement 20: Formatting Code with Black (APE 20)

This APE proposes that the astropy core package adopt Black formatting for the code. Black formatting refers to the default code style defined by the Black code formatter.

Since this APE was accepted in 2022, the Black code format has been implemented by other tools, most notably ruff. In the text below we will use the term Black to refer to Black or any other tool that provides robust auto-formatting in the Black code format. Beyond the initial migration of the code base to black formatting, the tool(s) used to maintain Black formatting is not a requirement of this APE.