In light of yesterday's entry , here is one of my newrules for Python modules, especially extension modules written in C:

If you're going to raise an exception because a system call failed,don't make up a new exception for it. Raise either IOError or OSError themselves.

Every deviation from this causes annoyancesfor Python programmers. This is especially visible in the situationwith signals and EINTR , where I really do not want tobe rewriting the same code over and over again with different exception

Why Should Engineers and Scientists Be Worried About Color? is abouthow straightforward use of colour in data visualizations can mislead youand hide information (and how to do better). Some of their examplesare eye-opening and alarming.

(Via Hacker News .)

(Since I took up photography I've had a muchincreased interest in how we perceive things, including colour.)

One of the interesting effects of setting a signal handler inyour Python program is, well, let me quote the signal module :

• When a signal arrives during an I/O operation, it is possiblethat the I/O operation raises an exception after the signal handlerreturns. This is dependent on the underlying Unix system's semanticsregarding interrupted system calls.

By 'an I/O operation' the manual means more than you might think; forexample, select.select() is affected by this.