On Dec 22, 2011 9:56 AM, "John O'Connor" <jxo6948@rit.edu> wrote:
I think the idea is that you ask for an attribute, which (in the less
common
cases) happens to be a multi-step lookup, and if the attribute is not found, you want it to return a default value *for the attribute you requested*, i.e. not a different value for any of the intermediate attributes, only a specific value that corresponds to the last attribute in the lookup chain. In the 99.9% case, that will be something like None or a "keep going, I don't care" value, not something that depends on the lookup path in any way.
I don't think the 0.1% case where you want more than that is worth a substantially more complicated API.
I could settle for the default= but I think it is too simple and thus incomplete. I think it is extreme to say that one default argument covers 99.9% use case. I do think you are right about the ignored path but that path may use more than one condition.
_xy = defaultattrgetter(('x', True), ('y', False)) x, y = _xy(foo) # usually do x unless told otherwise if x: ... # usually dont do y if y: ...
I guess one alternative could be: _xy = attrgetter('x', 'y', defaults={'x': True, 'y': False})
but that just looks like DRY without the D.
You could have attrgetter('x', 'y', defaults=(True, False)) to put the D back in. Arnaud