At 12:59 PM 7/21/2011 -0700, Reliable Domains wrote:

I assume that the implicit extend_virtual_paths() would be smart enough to only do real work if there are virtual packages to do it in, so much of the performance costs (bunch of stats) are bounded by the existence of and number of virtual packages that have actually been imported, correct?

Yes - this is true even for an explicit call. It only does this for imported virtual packages, and child virtual packages are only checked for if the parent package exists. So, in the case of a directory being added that has no parent packages, then the cost in stats is equal to the number of top-level, *imported* virtual packages. The __path__ wrapper scheme can do this even better, and defer doing any of the stat calls until/unless another import occurs for one of those packages. So if you munge sys.path and then don't import anything from a virtual package, no extra stat calls would happen at all.