On Tue, 29 Jul 2008 01:19:00 +0200, Anders J. Munch wrote: > Steven D'Aprano wrote: >> On Sun, 27 Jul 2008 23:45:26 -0700, Carl Banks wrote: >> >>> I want something where "if x" will do but a simple explicit test >>> won't. >> >> Explicit tests aren't simple unless you know what type x is. > > If you don't even know a duck-type for x, you have no business invoking > any methods on that object.
Have you tried to make "if x" fail? Pull open an interactive interpreter session and try. You might learn something. > If you do know a duck-type for x, then you also know which explicit test > to perform. > >> Explicit tests are not necessarily simple for custom classes. Testing >> for emptiness could be arbitrarily complex. That's why we have >> __nonzero__, so you don't have to fill your code with complex >> expressions like (say) >> >> if len(x.method()[x.attribute]) > -1 >> >> Instead you write it once, in the __nonzero__ method, and never need to >> think about it again. > > Okay, so you have this interesting object property that you often need > to test for, so you wrap the code for the test up in a method, because > that way you only need to write the complex formula once. I'm with you > so far. But then you decide to name the method "__nonzero__", instead > of some nice descriptive name? > What's up with that? Dude. Dude. Just... learn some Python before you embarrass yourself further. http://www.python.org/doc/ref/customization.html -- Steven -- http://mail.python.org/mailman/listinfo/python-list
