Parsimonious aims to be the fastest arbitrary-lookahead parser written
in pure Python and the most usable. It's based on parsing expression
grammars (PEGs), which means you feed it a simplified sort of EBNF
notation. Parsimonious was designed to undergird a MediaWiki parser
that wouldn't take 5 seconds or a GB of RAM to do one page, but it's
applicable to all sorts of languages.