How to properly subclass dict and override __getitem__ & __setitem__

What you're doing should absolutely work. I tested out your class, and aside from a missing opening parenthesis in your log statements, it works just fine. There are only two things I can think of. First, is the output of your log statement set correctly? You might need to put a logging.basicConfig(level=logging.DEBUG) at the top of your script.

Second, __getitem__ and __setitem__ are only called during [] accesses. So make sure you only access DictWatch via d[key], rather than d.get() and d.set()

Another issue when subclassing dict is that the built-in __init__ doesn't call update, and the built-in update doesn't call __setitem__. So, if you want all setitem operations to go through your __setitem__ function, you should make sure that it gets called yourself:

class DictWatch(dict):
    def __init__(self, *args, **kwargs):
        self.update(*args, **kwargs)

    def __getitem__(self, key):
        val = dict.__getitem__(self, key)
        print('GET', key)
        return val

    def __setitem__(self, key, val):
        print('SET', key, val)
        dict.__setitem__(self, key, val)

    def __repr__(self):
        dictrepr = dict.__repr__(self)
        return '%s(%s)' % (type(self).__name__, dictrepr)
        
    def update(self, *args, **kwargs):
        print('update', args, kwargs)
        for k, v in dict(*args, **kwargs).items():
            self[k] = v

Consider subclassing UserDict or UserList. These classes are intended to be subclassed whereas the normal dict and list are not, and contain optimisations.