George Sakkis wrote: > Martin v. Löwis wrote: >> Not-so-obviously, arbitrary user-defined values can also be >> treated as false: If they implement __nonzero__, they are >> false if False is returned from __nonzero__; otherwise, >> if they implement __len__, they are false if 0 is returned >> from __len__. Under these rules, array.array objects can >> also be false, as can UserList and UserDict objects. > > A notable exception are numarray arrays (probably true for numpy too, I > haven't tested it though): > >>>> from numarray import array >>>> bool(array([1,2])) > Traceback (most recent call last): > File "<stdin>", line 1, in ? > RuntimeError: An array doesn't make sense as a truth value. Use any(a) > or all(a).
numpy also has this behavior. Numeric yielded to the temptation to guess any(a) in the face of this ambiguity. Much buggy code was written as a result. -- 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 -- http://mail.python.org/mailman/listinfo/python-list
