Hi Luciano,

In chapter 22 you mention thatFrozenJSON.__getattr__() raising aKeyError is "not to confusing". However, today I discovered a side effect from this thatis confusing:copy.copy(FrozenJSON({'name': 'Jim Bo', 'class': 1982})) raises aRecursionError.

Indeed the documentation states that anAttributeError should be raised (https://docs.python.org/3/reference/datamodel.html#object.__getattr__) and apparently this is relied upon in the stdlib. In the copy implementation a new instance ofFrozenJSON is generated without the initializer being called. Then, when looking for some optional dunder methods (that are not found) the copy implementation triggers a__getattr__ call withself.__data not yet existing, triggering the recursion.

What I appreciate in your book is that you are always very precise about all types of unexpected side effects, so maybe you could consider spending some text on this in a future update.

Best regards, Michiel