First, don't appologize for asking questions. You read, you thought, and you tested. That's more than many people on this list do. Bravo!
One suggestion: when asking questions here it's a good idea to always briefly mention which version of python and what platform (linux, windows, etc) you're using. It helps us answer your questions more effectively. For testing performance the "timeit" module is great. Try something like: python -mtimeit -s 'import string;from myfile import isLower' "isLower('x')" You didn't mention the test data, i.e. the character you're feeding to isLower. It might make a difference if the character is near the beginning or end of the range. As to reasons to prefer one or another implementation, one *very* important question is "which one is clearer?". It may sound like a minor thing, but when I'm accosted first thing in the morning(pre-coffee) about a nasty urgent bug and sit down to pore over code and face "string.find(string.lowercase, ch) != -1", I'm not happy. Have fun with python! -- George Young -- http://mail.python.org/mailman/listinfo/python-list