You want to try out some new syntactic construction in Python but do NOT want to have to go through the trouble of
1. modifying Python's grammar file
2. modifying Python's lexer
3. modifying Python's parser
4. modifying Python's compiler
5. re-compile all the sources so as to create a new Python interpreter?
(These steps are described in these two blog posts.)
It can be done much more easily using any existing Python interpreter! ;-)
More details soon...