Python: magic methods that shouldn't be used

Question

I've created a class that is a tuple wrapper and tuples doesn't support item mutations. Should I leave __setitem__ and __delitem__ implementation or implement those methods like e.g. below (thus fall in kind of Refused Bequest code smell)? Which approach is more pythonic? Aren't custom exceptions better in such case?

def __setitem__(self, key, value):
    """
    :raise: Always.
    :raises: TypeError
    """
    self.data_set[key] = value  # Raise from tuple.

def __delitem__(self, key):
    """
    :raise: Always.
    :raises: TypeError
    """
    raise TypeError("Item deletion is unsupported")  # Custom exceptions thrown.

Answer 1

If your class is supposed to be a proper tuple subtype (according to Liskov substitution principle), then it should behave the same way as a tuple wrt/ to set/del - which as Guillaume mentions is the default behaviour if you just define neither __setitem__ nor __delitem__. I don't see how that would fall into the "Refused Bequest" category.

If your class uses a tuple as part of it's implementation but is NOT supposed to be a proper tuple subtype, then do whatever makes sense - but if you don't want to allow item assignment / deletion then again the simplest thing is to not implement them.