Atom allow to create memory efficient python object by specifying in the class the members (rather than allowing dynamic attributes). Atom can also be used to add type checking to object members. This goes against the notion of duck-typing but tends to make the code easier to read. Note also that metadata can be added to a member using the :py:meth:tag method. Metadata are extensively used in Exopy.
For clarity sake and Python2/3 compatibility, Unicode should be used instead of Str.