EmPy is a system for embedding Python expressions and statements in template
text; it takes an EmPy source file, processes it, and produces output. This is
accomplished via expansions, which are special signals to the EmPy system and
are set off by a special prefix (by default the at sign, @). EmPy can expand
arbitrary Python expressions and statements in this way, as well as a variety
of special forms. Textual data not explicitly delimited in this way is sent
unaffected to the output, allowing Python to be used in effect as a markup
language. Also supported are callbacks via hooks, recording and playback via
diversions, and dynamic, chainable filters. The system is highly configurable
via command line options and embedded commands.