Guido van Rossum wrote: > On 3/27/06, Travis Oliphant <[EMAIL PROTECTED]> wrote: > >>If you have Numeric or numpy installed try this: >> >>#import Numeric as N >>import numpy as N >> >>a = range(10) >>b = N.arange(10) >> >>a.__iadd__(b) >> >>print a >> >>Result: >> >>[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >> >> >>Contrast the returned output with >> >>import numpy as N >> >>a = range(10) >>b = N.arange(10) >> >>a += b >> >>print a >> >>Result: >> >>[ 0 2 4 6 8 10 12 14 16 18] >> >>Having "a+=b" and "a.__iadd__(b)" do different things seems like an >>unfortunate bug. >> >>It seems to me that the problem is that the INPLACE_ADD and >>INPLACE_MULTIPLY cases in ceval.c use PyNumber_InPlace<YYY> instead of >>trying PySequence_InPlace<YYY> when the object doesn't support the >>in-place number protocol. >> >>I could submit a patch if there is agreement that this is a problem. > > Well how is the interpreter to know whether += meanse numeric add or > sequence add in any particular case? > > Shouldn't it be numpy's responsibility to implement both operations > identically?
"a" is a list object. Travis's question is, "why doesn't the list object implement both operations identically?" I think the answer is, "it never gets a chance to." When a numpy array is on the LHS of an inplace operation, we always want the numeric add. numpy arrays can't be extended inplace like a list, and a lone "+" is always a numeric operation for arrays, never a sequence operation. When numpy arrays are on the LHS of an inplace operation, everything works consistently. The issue seems to arise from the fact that PyNumber_InPlaceAdd tries to coerce the LHS and the RHS to a common numerical type first before trying PySequence_InPlaceConcat. Lists of numbers coerce to numpy arrays just fine, so this code path is taken, and nothing tests for the sq_inplace_concat or sq_concat slots. Personally, I'm willing to just document it in the numpy documentation as a rarely-seen gotcha. This behavior pretty much affects just us. -- Robert Kern [EMAIL PROTECTED] "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
