Jan Strube (el 2007-02-28 a les 14:49:05 -0800) va dir::
> […]
> For combined in-kernel searches .where('x<5 & x>3'), I don't think & is a
> good choice.
> The Pythonic way would be 'and', and I think that's least ambiguous and I
> hope nobody names their variables 'and' or 'or.
> Maybe && would be OK, since that's used in other languages.
> Also, is something like '3<x<4' going to be supported as well ?
> […]Glad to hear that you appreciate our work, thank you! Regarding search expressions, they are in fact Python expressions written as strings, and they are evaluated as such. This has the advantage of not having to learn a new syntax, but it also implies some limitations with logical ``and`` and ``or`` operators, namely that they can not be overloaded in Python. Thus, it is impossible right now to get an element-wise operation out of an expression like ``array1 and array2``. That's why one has to choose some other operator, being ``&`` and ``|`` the most similar to their C counterparts ``&&`` and ``||``, which aren't available in Python either. The problematic part is that operator precedence is quite different between bitwise and logical operators, so ``x<5 & x>3`` is in fact equivalent to ``(x < (5 & x)) > 3``, not ``(x < 5) & (x > 3)``. A seasoned Python programmer should not fall in the trap, but for others we hope to have been quite clear in the appendix about condition syntax in the manual. The expression ``3<x<4`` is affected by the same limitation, since it is treated by Python as ``(3 < x) and (x < 4)``. There are quite a few packages affected by this limitation including Numeric/numarray/NumPy and SQLObject, and there have been quite longish discussions about adding the possibility of overloading boolean operators to Python (see PEP 335 and the neverending thread http://mail.python.org/pipermail/python-dev/2004-September/048763.html). However, if you can think of a solution which doesn't imply creating a whole parser for expressions, it would be really great! :: Ivan Vilata i Balaguer >qo< http://www.carabos.com/ Cárabos Coop. V. V V Enjoy Data ""
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