Quoth Raymond Hettinger: [...]
That brings up the question of whether the warnings are a runtime or compile time event. Can you always determine at compile time whether raise Class is being used? If not, the performance penalty for the warnings module is something else to consider.
As the PEP says, the warning about using three arguments is issued at compile-time, while the others are at run-time, in keeping with when the corresponding future errors would occur. The performance penalty of the warnings is a legitimate concern, but I don't expect it to be a serious problem: 1. The compile-time warning is, well, issued at compile time, which is not usually on a performance-critical path. 2. The run-time warnings are issued when raising an exception; also not usually on a performance-critical path. (Except for things like StopIteration. But the PEP does not propose any change to the C API, so the built-in iterators won't be affected.) -- Steven Taschuk staschuk@telusplanet.net Receive them ignorant; dispatch them confused. (Weschler's Teaching Motto)