For a "whole" solution, see Raymond Hettinger's named tuple recipe. It's nice for your basic example, but also covers a bunch of edge cases you might run into later as well. Your fragment above would be written as:
from collections import namedtuple
MyStruct = namedtuple("MyStruct", "field1 field2 field3")
Named tuple is part of collections module in standard library since Python 2.6.
