On Sat, Sep 10, 2011 at 12:07 PM, Massimo Di Pierro <mdipierro@cs.depaul.edu> wrote:

Not to open a can of worms but why not use eval in this example? It is faster. It is 5x more compact. It allows me to take advantage of the Python parser instead of reinventing the wheel. It is less error prone and easier to understand. It is a python keyword.

It is unsafe (as the bug in your first version inadvertently illustrated :-). I don't actually quite follow what your example does (sorry), but, even though it is less powerful than exec(), eval() invokes the full Python parser+compiler, which can take quite a bit of time to start up and uses a fair bit of memory. Also in other Python versions this is often much slower than in CPython, or has a big startup overhead. But, of course, it is great for quick demos! -- --Guido van Rossum (python.org/~guido)