On 8/24/2010 12:40 AM, python-dev-requ...@python.org wrote:
Message: 4 Date: Mon, 23 Aug 2010 17:21:50 -0700 From: Brett Cannon
<br...@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
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