A recent commentator on HowNotToDoDNSI has prompted me to write aboutthe hell that glue records could be in in the Internet's old days. Toreally cover the horror, I'll start with the ordinary glue recordhorror.

Glue records are additional A records that get returned by higherlevel nameservers when people ask for NS records to avoid recursionproblems that would otherwise ensue when, eg, foo.com has www.foo.com as its nameserver. This can be exploited to optimize DNSlookups a bit, as

Is concurrency hard? You can certainly find people arguing both sidesof the issue if you look hard enough (mostly for rather than against).But I think the question may be blurring two things together that areworthwhile to separate: 'concurrency is difficult to learn andunderstand', and 'concurrency is tricky to implement correctly'.

For example, in his reaction to Joel Spolsky's Java Schools article ,Tim Bray gives a little taxonomy of difficulty:

My experience differs from Joel's in another respect:

Something I took from this Ian Bicking entry is that synergies and elegance don't just happen; someone usually workedhard to make it all come out neatly. Python lists have an interestingcase of this; some apparently odd decisions in other places turn out tobe needed to create useful (and error-avoiding )synergies.

Python lists (and sequences in general) are indexed from 0. Zero-basedindexing presents a problem, which can be succinctly stated as this:list element indexes run from 0 to len