On Mon, Oct 6, 2008 at 14:32, John <[EMAIL PROTECTED]> wrote: > hi, > > why does the ValueError appear below, and how can i make that 2<a<5 > expression work when a is an array?
(2<a<5) evaluates to ((2<a) and (a<5)). The "and" keyword coerces its arguments to actual boolean True or False objects, so this is actually (bool(2<a) and bool(a<5)). Arrays implement rich comparisons, so if 'a' is an array, then (2<a) is an array of bools. bool(some_array) is ambiguous; sometimes you want it to be True if any of the elements are True and sometimes you only want it to be True if all of the elements are True. Consequently, numpy refuses to guess what you want and makes you specify with the .any() and .all() methods. Unfortunately, this means that (2<a<5) will never work for arrays. -- 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
