getattr takes a third parametergetattr(obj, attribute_name, default) is like:
try:
return obj.attribute
except AttributeError:
return default
except that attribute_name can be any string.
This can be really useful for duck typing. Maybe you have something like:
class MyThing:
pass
class MyOtherThing:
pass
if isinstance(obj, (MyThing, MyOtherThing)):
process(obj)
(btw, isinstance(obj, (a,b)) means isinstance(obj, a) or isinstance(obj, b).)
When you make a new kind of thing, you'd need to add it to that tuple everywhere it occurs. (That construction also causes problems when reloading modules or importing the same file under two names. It happens more than people like to admit.) But instead you could say:
class MyThing:
processable = True
class MyOtherThing:
processable = True
if getattr(obj, 'processable', False):
process(obj)
Add inheritance and it gets even better: all of your examples of processable objects can inherit from
class Processable:
processable = True
but you don't have to convince everybody to inherit from your base class, just to set an attribute.