test ( test ( name 'bob# name 'sueprint( nameworks fails age # age print( ageworks fails in factthis is first-cut solution for an implementation of attribute privacy in python --disallowing changes to attribute names outside class although python doesn' support private declarations per setechniques like this can emulate much of their purpose this is partial--and even clumsy--solutionthoughto make it more effectivewe must augment it to allow classes to set their private attributes more naturallywithout having to go through __dict__ each timeas the constructor must do here to avoid triggering __setattr__ and an exception better and more complete approach might require wrapper ("proxy"class to check for private attribute accesses made outside the class onlyand __getattr__ to validate attribute fetches too we'll postpone more complete solution to attribute privacy until where we'll use class decorators to intercept and validate attributes more generally even though privacy can be emulated this waythoughit almost never is in practice python programmers are able to write large oop frameworks and applications without private declarations--an interesting finding about access controls in general that is beyond the scope of our purposes here stillcatching attribute references and assignments is generally useful techniqueit supports delegationa design technique that allows controller objects to wrap up embedded objectsadd new behaviorsand route other operations back to the wrapped objects because they involve design topicswe'll revisit delegation and wrapper classes in the next string representation__repr__ and __str__ our next methods deal with display formats-- topic we've already explored in prior but will summarize and formalize here as reviewthe following code exercises the __init__ constructor and the __add__ overload methodboth of which we've already seen (is an in-place operation herejust to show that it can beper named method may be preferredas we've learnedthe default display of instance objects for class like this is neither generally useful nor aesthetically prettyclass adderdef __init__(selfvalue= )self data value initialize data string representation__repr__ and __str__