It's not a Python thing, though. It's a reStructuredText thing. I don't see how this syntax is more "magic" than, say, using # in Markdown to indicate a heading

It's not a Python thing, though. It's a reStructuredText thing. I don't see how this syntax is more "magic" than, say, using # in Markdown to indicate a heading. The reason it's a double colon is because a single colon acts like a normal single colon (i.e., it's not interpreted in any way), which is sometimes what you want (i.e., not every indented block is a code block).