[Python-ideas] Specifying Python version

[MRAB]

Instead of verbatim identifiers, how about a special comment giving the 
Python version in which the file was written?

There could then be a tool similar to 2to3 that converts the file to a 
more recent version of Python that might have new reserved words. In 
most cases the new file would merely be a copy of the original, but with 
an updated Python version.