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.