How can I create an object and add attributes to it?

Question

I want to create a dynamic object (inside another object) in Python and then add attributes to it.

I tried:

obj = someobject obj.a = object() setattr(obj.a, 'somefield', 'somevalue') 

but this didn't work.

Any ideas?

edit:

I am setting the attributes from a for loop which loops through a list of values, e.g.

params = ['attr1', 'attr2', 'attr3'] obj = someobject obj.a = object()  for p in params:    obj.a.p # where p comes from for loop variable 

In the above example I would get obj.a.attr1, obj.a.attr2, obj.a.attr3.

I used the setattr function because I didn't know how to do obj.a.NAME from a for loop.

How would I set the attribute based on the value of p in the example above?

Answer 1

The built-in object can be instantiated but can't have any attributes set on it. (I wish it could, for this exact purpose.) It doesn't have a __dict__ to hold the attributes.

I generally just do this:

class Object(object):     pass  a = Object() a.somefield = somevalue 

When I can, I give the Object class a more meaningful name, depending on what kind of data I'm putting in it.

Some people do a different thing, where they use a sub-class of dict that allows attribute access to get at the keys. (d.key instead of d['key'])

Edit: For the addition to your question, using setattr is fine. You just can't use setattr on object() instances.

params = ['attr1', 'attr2', 'attr3'] for p in params:     setattr(obj.a, p, value) 

Answer 2

You could use my ancient Bunch recipe, but if you don't want to make a "bunch class", a very simple one already exists in Python -- all functions can have arbitrary attributes (including lambda functions). So, the following works:

obj = someobject obj.a = lambda: None setattr(obj.a, 'somefield', 'somevalue') 

Whether the loss of clarity compared to the venerable Bunch recipe is OK, is a style decision I will of course leave up to you.