On 31/07/2010 16:07, Nick Coghlan wrote:
On Sat, Jul 31, 2010 at 3:57 PM, Daniel Waterworth
<da.waterwo...@gmail.com> wrote:
@Nick: I suppose the simplest way to detect re-importation in the
general case, is to store a set of hashes of files that have been
imported. When a user tries to import a file where it's hash is
already in the set, a warning is generated. It's simpler than trying
to figure out all the different ways that a file can be imported, and
will also detect copied files. This is less infrastructure than you
were suggesting, but it's not a perfect solution.
Hashing every file on import would definitely be more overhead than
just checking __file__ values (since we already calculate the latter,
and regardless of how a file is imported, it needs to end up in
sys.modules eventually). Besides, importing the same code under
different names happens in several places in our own test suite (we
use it to check that code behaviour doesn't change just because we
import it differently), so we can hardly disable that behaviour.
That said, I really don't think catching such a rare error is worth
*any* runtime overhead. Just making "__main__" and the real module
name refer to the same object in sys.modules is a different matter,
but I'm not confident enough that I fully grasp the implications to do
it without gathering feedback from a wider audience.
Some people workaround the potential for bugs caused by __main__
reimporting itself by doing it *deliberately*. Glyf even recommends it
as good practise. ;-)
http://glyf.livejournal.com/60326.html
So - the fix you suggest would *break* this code. Raising a warning
wouldn't... (and would eventually make this workaround unnecessary.)
Michael
Cheers,
Nick.
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