Ganesh Gopalakrishnan <gan...@cs.utah.edu> writes:
> This probably is known, but a potential pitfall (was, for me) nevertheless.
> I suspect it is due to hash collisions between 's3' and 's13' in this
> case?
What is the actual problem? What behaviour is occurring that doesn't
match your expectation?
> >>> S1==S2
> S1==S2
> True
> >>> str(S1)
> str(S1)
> "{'s8', 's13', 's2', 's0', 's7', 's6', 's4', 's3', 's14'}"
> >>> str(S2)
> str(S2)
> "{'s8', 's3', 's2', 's0', 's7', 's6', 's4', 's13', 's14'}"
> >>> str(S1) == str(S2)
> False
Right, that's all correct (though I don't know why some of your
expressions are being shown twice). A deliberate property of a set is
that its items are unordered.
<URL:http://docs.python.org/library/stdtypes.html#set>
Since sets are unordered, the string representation may show the items
in an arbitrary and unpredictable sequence. Don't write any code that
depends on a predictable sequence of retrieval from an unordered
collection.
So what did you expect instead, and what supports that expectation?
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Ben Finney
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