On 9/30/05, Raymond Hettinger <[EMAIL PROTECTED]> wrote: > [Guido van Rossum] > > __len__ is for sequences and mappings specifically -- everything that > > supports __getitem__ should have __len__ and everything that has > > __len__ should have __getitem__. > > That's going a bit far. Unordered collections (like sets and bags) are > a good counter-example. >
I've implemented many extension types in C, always to interface external libraries (the main examples, MPI and PETSc). In those libraries, some object are invalid (MPI_COMM_NULL) or can get deallocated in the C side. I always implement a __nonzero__ method for testing those situations. It sounds a bit bizarre to me to have to implement a number method for a object that is far from being a number, and of course __len__ do not make any sense. Perhaps Py3k could have a more explicit mechanism for definig the truth value of an object? Something like __bool__ method to be filled in type object? Any opinions? Lisandro Dalcín _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
