On 9/17/07, Mathieu Fenniak <[EMAIL PROTECTED]> wrote: > On 17-Sep-07, at 9:00 AM, Guido van Rossum wrote: > > Maybe I should apologize for pushing back so hard, but in my > > experience most people who subclass a built-in type do it because they > > can, not because they should -- the lamented "path" module being a > > prime example in my view. > > > > I'm still not convinced of the usefulness in your case -- what would > > you lose if you just passed a bytes instance around instead of an > > instance of the subclass you'd like to have? > > The builtin type subclasses in pyPdf (including the would-be bytes > subclass) add additional methods that every pdf object is expected to > support. All the PDF object types have two additional methods > (writeToStream and getObject) that have varying behavior for each > class: (relatively inconsequential PDF information follows) > > "writeToStream" method that serializes the object -- a byte string > would write out <68656c6c6f>, a text string (hello), and so on for > other more complex types (dictionaries, labels, arrays, PDF data > streams). The type is also responsible for encrypting itself when > applicable.
This sounds like a perfect application for generic functions instead of subclassing. > PDF files also have an ability to reference objects elsewhere in the > file. For example, the length of a content stream can be a simple > "500 bytes", or it can be "read this length at offset X in the > file". Since almost any object can be an indirect object reference, > the library objects support a "getObject" method that returns self -- > excluding PDF "indirect object reference" objects, which read an > object from a table in a PDF file. Similar. > If you decide that bytes should be subclassable, I've included with > this e-mail a patch that adds the basetype bit, adds some unit tests > for bytes subclasses, and includes __dict__ in the bytes_reduce > method (for pickling subclass instances). I was going to upload this > to the SF patch manager, but it appears to be closed to permit only > project members access. > > Mathieu Fenniak > > > -- --Guido van Rossum (home page: http://www.python.org/~guido/) _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
