Hello Bengt, On def chr(i): return "\x00\x01\x02x03...\xFF"[i] versus def chr(i): return'%c' % i I feel the second solution to be more to the point. The first one seems redundant somehow: "pick the ith character from this string whose ith character just happen to have ASCII code i". But that's probably a minor point. It shows that chr() may well be implemented in pure Python using lower "primitives" (let's call them built-in functions or methods). It may indeed be a good idea to draw a fluctuating but documented dependency graph between pure Python and built-in functions. It would let two teams work on these two halves of the work: (1) writing pure Python functions (as Scott did), and (2) writing built-in functions. I think that Scott's work drew the line for the built-in functions. Most of what he couldn't code must be done as built-in functions. Armin.