On 8/24/2010 12:40 AM, python-dev-request@python.org wrote:
Message: 4 Date: Mon, 23 Aug 2010 17:21:50 -0700 From: Brett Cannon <brett@python.org> It is also non-obvious to any beginner. Are we really going to want to propagate the knowledge of this trick as a fundamental idiom? I would rather leave hasattr in that instance. But I'm +1 on only swallowing AttributeError.
I'd argue that since the ability to inherit a class from "dict" was added, dynamically adding attributes is somewhat obsolete. An object instance is not a dictionary. Especially since its namespace interacts with the namespace of its class. I've been using Google Code Search to look at the actual use cases for "setattr". The main uses are: 1. Copying. Object copying is done with "setattr". All the "setattr" objects occur during object construction, or shortly after. 2. Creating proxy objects for remote access. This is much like copying, 3. Representing HTML objects as Python object. This usually requies gyrations to avoid clashes with Python built-in names and functions; "class" is a common attribute in HTML, and a reserved word in Python, and some hack is necessary to make that work. BeautifulSoup does this. It's rare that attributes are added long after object construction. Perhaps a mechanism should be provided for dynamically constructing an object. Something like class foo(object) : pass attrdict = { a : 1, b : 2} make_object(foo, attrdict) This covers most of the use cases for "setattr". John Nagle