Beginners and experts (Batchelder blog post)

[Gregory Ewing]

Steve D'Aprano wrote:
> (1) I know there's a bug in a specific chunk of code, but I'm having trouble
> working out where. When everything else fails, if I perturb the code a bit
> (reorder lines, calculate things in a different order, rename variables, etc)
> it may change the nature of the bug enough for me to understand what's
> happening.

 > Its an experiment, but not really "carefully designed".

I think it's more carefully designed than you give it credit for.
You still need to understand quite a lot about the program to know
what changes are likely to yield useful information, and how to
interpret the results.

> Its more like "what
> happens if we hit this bit with a hammer?"

In biology it's called a "shotgun experiment". "If we blast this
bit of DNA with radiation, what part of the organism does it
mess up?"

> (2) I hate off by one errors, and similar finicky errors that mean your code is
> *almost* right. I especially hate them when I'm not sure which direction I'm
> off by one. If you have unit tests that are failing, sometimes its quicker and
> easier to randomly perturb the specific piece of code until you get the right
> answer, rather than trying to analyse it.

With off-by-one errors it's still pretty specific -- start
the loop at 1 instead of 0, etc.

But in cases like that I prefer to rewrite the code so that
it's obvious where it should start and finish.

> The complexity of code increases faster than our ability to manage that
> complexity.

And then there's "If you write the code as cleverly as you can,
you won't be smart enough to debug it!"

-- 
Greg