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 ...