On Mon, Jun 07, 2010 at 02:37:27PM -0700, Robert Bradshaw wrote: > On Jun 7, 2010, at 6:12 AM, Florent Hivert wrote: > >> Hi there, >> >> I've question concerning handling of hash value vs portability. Is sage >> developer guide manual one can read: >> >> Here is the definition of __hash__ from the Python reference manual. >> >> Called for the key object for dictionary operations, and by the >> built-in function hash(). Should return a 32-bit integer usable as >> a >> hash value for dictionary operations. >> >> However with ipython (on a 64 bits machine): >> >> In [1]: hash(None) >> Out[1]: 140504985179472 >> >> which definitely does looks like a 32 bit value. Moreover, it seem that in >> python ref man, [2], the sentence about 32-bits has been removed. So I >> have >> two questions: >> >> 1. I think we should update the devguide, or is there something I don't >> get ? > > No, we should update the developers guide. Despite this sentence, the (c) > return type of "hash" has been a long since Python 2.3 at least, so I think > this wasn't ever correct for 64-bit long machines. (What was required is > that it fit into a Python int.) > >> 2. I'm writing a Cython class which caches the hash value. Which type >> should I >> use for the attribute ? int doesn't work since when trying to store the >> hash of None in an int I get >> >> OverflowError: value too large to convert to int >> >> Is long ok and portable (it is was is used in a few place in sage) ? >> Should >> we write it in the doc ? > > Yes, we should be using C longs here. Under the hood > > Python int = C long != C int > Python float = C double != C float > > and Python longs have no (native) C equivalent.
Thanks for those explanations... I'll take care of that on #9181 Florent -- 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
