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It takes me 10 seconds to run 2to3 on the example file.

Yes, and each new fixer makes it slower. The biggest problem is the
pattern matching system, which tends to take 99% of the running time.
I've talked to several people who are interested in optimizing 2to3 as a
GSoC project, though, so I anticipate some speed ups coming through that.

Martin and I talked about this, and I'm going to try loading the first 
node of each tree generated by the PATTERNs into a dictionary, then when 
the tree is walked, only fixers which could potentially match the current 
node are executed.

Keep in mind that not all fixers use PATTERN, for example fix_ne.

A patch so that, on each node, only fixers who's head node could match 
this node are executed. It's still hacky and ugly, but a decent POC.

With the patch applied, all tests in test_fixers fail.

Ah, yea -- in my rush to catch my train I must have neglected to look at 
the _results_ of running test.py... I have updated the patch so the fixers 
will work.

The updated version of the patch passes the tests and yields a 19-20%
speed increase in the running time of test_all_fixers and the time taken
for 2to3 to translate itself. I've sent David some comments on the
patch, and once it's cleaned up some, this will be checked in.
I'd like to keep the issue open, since there are clearly additional
speed increases to be made.

I've cleaned up and applied the patch in r62470.
As Collin suggested, I'm leaving the ticket open to use in the future.

I think we can safely say this has been fixed especially with regards to
fix_imports. Thanks to Nick Edds! It only takes me about 3 seconds to
process the example file.