test.py

mydict = {'mykey': 'foo', }


class MyObj(object):
    thing = 'whatever'

myobj = MyObj()

val = None
try:
    val = getattr(myobj, 'thing', mydict['nonexistent'])
except KeyError as e:
    val = getattr(myobj, 'thing', None)
    if not val:
        raise e

print val