On Wed, 2005-10-26 at 09:00 -0700, Stephen Walton wrote:
Arnd Baecker wrote:
I also think that double should be kept as default. If I understand things correctly, both normal python and all the libraries for scipy can only deal with that at the moment.
I respectfully disagree that double should be the default target for upcasts. This is a holdover from C and was a bad decision when made for that language. And, as Pearu points out, it has dire consequences for storage. If I get a 16 Megapixel image from HST with two-byte integers, I definitely would not want that image upcast to 64 or, heaven forfend, 128 bits the first time I did an operation on it.
I think there are two goals here: 1) it just works 2) it is efficient. These goals are not always compatible. In order to just work, certain defaults need to be assumed. Python works like that, it is one of the reasons it is so convenient. On the other hand, efficiency, space efficiency in particular, requires greater control on the part of the programmer who has to take the trouble pick the types he wants to use, making a trade between precision, space, and speed. So I think that we should choose reasonable defaults that carry on the Python spirit, while leaving open options for the programmer who wants more control. How to do this without making a mess is the question. Now, python does the following:
from math import * sqrt(2) 1.4142135623730951
and if we are going to overload sqrt we should keep this precision. Do we really want to make a distinction in this case between math.sqrt and Numeric.sqrt ? I myself don't think so. On the other hand, it is reasonable that scipy not promote float types in this situation. Integral types remain a problem. What about uint8 vs uint64 for instance? Maybe we should either require a cast of integral types to a float type for arrays or define distinct functions like sqrtf and sqrtl to handle this. I note that a complaint has been made that this is unwieldy and a throwback, but I don't think so. The integer case is, after all, ambiguous. The automatic selection of type only really makes sense for floats or if we explicitly state that maximum precision, but no more than necessary, should be maintained. But what happens then for int64 when we have a machine whose default float is double double? Chuck