Hi.
I've been working on fixing the Python 3.3 issues, most of which stem
from hash randomization. I was thinking, instead of trying to fix
every algorithm that recurses through .args, it would be easier to
just make .args canonical. Are there any suggestions on a key that we
could use to sort the args for Add and Mul that would be just as fast
as hash, but be the same everywhere?
I was thinking of using _hashable_content. This should be identical
to sorting by hash, in the sense that the has is computed from the
_hashable_content, but unlike the hash, it will always compare the
same everywhere. There are a few issues with this idea:
1. The hash is not exactly computed from _hashable_content. Rather,
the args are in _hashable_content, and the name of the object is
injected manually by __hash__. Assumedly this can be fixed, though.
2. This would put a restriction on _hashable_content that it must not
only be hashable, but also comparable. This is not an issue now, as
far as I can tell, because it consists only of tuples, ints, and
strings, but for example if we ever wanted to use frozenset, we
wouldn't be able to (we'd rather have to sort it into a tuple, which
could potentially be a performance issue). I haven't made a deep
study of _hashable_content yet, but I don't think this is currently an
issue, but I'm wondering if anyone can foresee it being one.
3. I made a change to use this, and from what I can tell, it isn't
slower, but I'm not 100% convinced on my benchmarking. Can anyone
suggest any benchmarks that would be good to test this? So far, I've
been testing
a = [Symbol('x%d' %i) for i in xrange(10000)]
random.shuffle(a)
Mul(*a)
Add(*a)
using IPython's %timeit magic, and there seems to be no significant
difference. If anyone can suggest a better way to test it, let me
know. Or better yet, test it yourself. I'll post a PR that
implements it as soon as I change _hashable_content to include the
name (hopefully that won't be too difficult).
Aaron Meurer
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