Ian Bicking: the old part of his blog

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Don't forget that there *will* be improvements - on many of my perl-to-python rewrites, I've found things that could never have worked, done a little experimenting and confirmed that indeed, they hadn't, and fixed them as part of the rewrite. Some of this is purely due to paying new attention to the code - some of it, though, can be creditted to "explicit rather than implicit" and the way you expose certain things.

This tricky part is not taking the temptation to improve beyond that. If you're being especially rigorous, the experimenting above goes in the test suite, to explicitly show what wasn't working before...
Comment on Rewriting and Refactoring
by Mark Eichin