Patches item #1548082, was opened at 2006-08-28 12:38
Message generated for change (Comment added) made by rhettinger
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Category: Core (C code)
Group: Python 3000
Status: Open
Resolution: None
Priority: 5
Submitted By: Georg Brandl (gbrandl)
Assigned to: Guido van Rossum (gvanrossum)
Summary: "if x in setliteral" peepholer optimization
Initial Comment:
Like "for x in tuple_or_list", this patch rewrites "for
x in set" to use a constant frozenset.
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>Comment By: Raymond Hettinger (rhettinger)
Date: 2006-08-29 16:26
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This implementation too simplistic, you need to use a
subclass of frozenset that overrides the __contains__()
method to return False when the argument is not hashable.
Otherwise, you end-up with a semantic change for:
x = {}
if x in [1,2,3]:
print 'Not Found'
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Comment By: Georg Brandl (gbrandl)
Date: 2006-08-29 14:08
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Argh. Like in the py3k mail, I confusedly interchanged "for
x in set" and "if x in set".
if x in [1,2,3] does get special treatment, and optimizing
the "in" test does make sense.
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Comment By: Guido van Rossum (gvanrossum)
Date: 2006-08-29 13:24
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Um, "for x in [1,2,3]" doesn't get any treatment. What would
be the point of writing "for x in {1,2,3}" anyway?
I'd rather reject this as premature optimization.
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