I want to dynamically query which objects from a class I would like to retrieve. getattr seems like what I want, and it performs fine for top-level objects in the class. However, I'd like to also specify sub-elements.

class MyObj(object):def __init__(self):self.d = {'a':1, 'b':2}self.c = 3myobj = MyObj()
val = getattr(myobj, "c")
print val # Correctly prints 3
val = getattr(myobj, "d['a']") # Seemingly incorrectly formatted query
print val # Throws an AttributeError

How can I get the object's dictionary elements via a string?

The reason you're getting an error is that getattr(myobj, "d['a']") looks for an attribute named d['a'] on the object, and there isn't one. Your attribute is named d and it's a dictionary. Once you have a reference to the dictionary, then you can access items in it.

mydict = getattr(myobj, "d")
val    = mydict["a"]

Or as others have shown, you can combine this in one step (I showed it as two to better illustrate what is actually happening):

val = getattr(myobj, "d")["a"]

Your question implies that you think that items of a dictionary in an object are "sub-elements" of the object. An item in a dictionary, however, is a different thing from an attribute of an object. (getattr() wouldn't work with something like o.a either, though; it just gets one attribute of one object. If that's an object too and you want to get one of its attributes, that's another getattr().)

You can pretty easily write a function that walks an attribute path (given in a string) and attempts to resolve each name either as a dictionary key or an attribute:

def resolve(obj, attrspec):for attr in attrspec.split("."):try:obj = obj[attr]except (TypeError, KeyError):obj = getattr(obj, attr)return obj

The basic idea here is that you take a path and for each component of the path, try to find either an item in a dictionary-like container or an attribute on an object. When you get to the end of the path, return what you've got. Your example would be resolve(myobj, "d.a")