On Sun, Jul 25, 2010 at 8:11 PM, Dan Drake <dr...@kaist.edu> wrote: > On Sun, 25 Jul 2010 at 07:11PM -0700, Carl Witty wrote: >> Hmm... looks like the current state of affairs is a mess. Looking >> through the 'def __hash__' grep hits in sage/rings, there are quite a >> few of each of the following: >> >> 1) no doctest at all >> 2) provide both 32-bit and 64-bit doctests >> 3) define your hash function to produce a 32-bit output that's the >> same on 32-bit and 64-bit systems; doctest an instance of that output >> 4) doctest hash value equality without ever showing a doctest output >> >> plus one instance where the hash output is marked "# random". >> >> So whatever you do with this particular patch, it won't make things >> much worse :) > > Yeah! That's what I like to hear. :) > >> As for the desired state of affairs: I have a slight preference for >> providing both 32-bit and 64-bit doctest outputs, because it increases >> our chance of noticing if something changes unexpectedly. But I could >> also make a good case for only testing hash equality, because it >> slightly reduces the effort involved in changing hash functions, >> internal representations, etc. :) > > If the hash values are supposed to be 32- or 64-bit integers, perhaps > testing that would be useful; something like > > sage: hash(foo) > 0 and is_integer(hash(foo)) > True > sage: hash(foo) < 2^sys_bits() > True > > where sys_bits() is a function that we could add that returns "32" or > "64", depending on your system. (Maybe such a function is already in > Sage.) Or we could just do two tests: > > sage: hash(foo) < 2^32 # 32-bit > True > > and so on. The above setup ignores the particular value and instead > insures that it has the necessary properties, which I think is what we > really want. Thoughts?
1) We want more properties than that; a constant hash (that returned 17 for all elements of a given ring) would not be so useful. (Of course, very few (possibly none?) of the existing doctests test for non-constant hashes.) 2) The Python code in hash() that calls your __hash__ method already enforces your properties (hashes must be integers, and if they're not in the correct range, Python will re-hash them into a small enough integer). So just having hash(foo) not return an error is enough to check those properties. Carl -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
