isinstance() bug

[Skip Montanaro]

    Sidharth> python is a dynamic language it figures out where modules are
    Sidharth> located at run time, it would be expensive to check all paths
    Sidharth> to see if they ended up at the same file.

Maybe not:

    Help on function abspath in module posixpath:

    abspath(path)
        Return an absolute path.

Considering all the other stuff import has to do, this seems like only a
small extra bit of work.

Skip