Question

I’ve set up a custom namespace lookup dictionary in order to map elements in XML files to subclasses of ObjectifiedElement. Now, I want to add some data to instances of these classes. But due to the way ObjectifiedElement works, adding an attribute will result in an element being added to the element tree, which is not what I want. More importantly, this doesn’t work for all Python types; for example, it is not possible to create an attribute of the list type.

This seems to be possible by subclassing ElementBase instead, but that would imply losing the features provided by ObjectifiedElement. You could say I only need the read part of ObjectifiedElement. I suppose I can add a __getattr__ to my subclasses to simulate this, but I was hoping there was another way.

Answer 1

I ended up with having __getattr__() simply forward to etree’s find():

class SomewhatObjectifiedElement(etree.ElementBase):
    nsmap = {'ns': 'http://www.my.org/namespace'}

    def __getattr__(self, name):
        return self.find('ns:' + name, self.nsmap)

This will only return the first element if there are several matching, unlike ObjectifiedElement‘s behaviour, but it suffices for my application (mostly it can be only a single match, otherwise, I use findall()).