On Wed, Oct 29, 2008 at 22:37, Alan G Isaac <[EMAIL PROTECTED]> wrote: > On 10/29/2008 3:43 PM Robert Kern wrote: >> The defining characteristic is >> that "x <op>= y" should be equivalent to "x = x <op> y" except >> possibly for *optional* in-place semantics. > > This gets at a bit of the Language Reference that I've > never understood. > > when possible, the actual operation is performed > in-place, meaning that rather than creating a new > object and assigning that to the target, the old > object is modified instead. > > What does that mean? I assume "when possible" means in part > "when mutable", ruling out e.g. Python integers or floats.
In part, yes. But also "when possible" excludes in-place matrix multiplication on ndarrays since we don't, as numpy policy, resize ndarrays implicitly. > But the rest does not really seem part of the language, but > rather seems to be normative? That is, I could define > __iadd__ anyway I want. Is the above saying that I "should" > define __iadd__ to do an in-place operation "if possible". > If so, why is such a normative statement part of the > language reference? Or is it a statement about the language > that I'm just not getting? It is a guide to the intended usage of the feature. You can see other such guides in the documentation for __repr__, for example. The use of the word "should" is not rigidly consistent throughout the document. In other places, it is closer to the meaning of MUST in RFC 2119: http://www.faqs.org/rfcs/rfc2119.html The reason such guides are in the reference manual is because ... well, where else are you going to put them? Describing the use case of a feature is, in this case I think, essential to describing the feature. You have to explain why one would bother defining __iadd__ if one already had __add__. Similarly, you have to explain why one would use __repr__ over __str__ or vice versa. -- Robert Kern "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 _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
