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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _execute_callback(self, *args):
        "Executes the callback with the appropriate args and kwargs"
        self._validate_key(args)      # Validate input key

        # Additional validation needed to ensure kwargs don't clash
        kdims = [kdim.name for kdim in self.kdims]
        kwarg_items = [s.contents.items() for s in self.streams]
        hash_items = tuple(tuple(sorted(s.hashkey.items())) for s in self.streams)+args
        flattened = [(k,v) for kws in kwarg_items for (k,v) in kws
                     if k not in kdims]

        if self._posarg_keys:
            kwargs = dict(flattened, **dict(zip(self._posarg_keys, args)))
            args = ()
        else:
            kwargs = dict(flattened)
        if not isinstance(self.callback, Generator):
            kwargs['_memoization_hash_'] = hash_items

        with dynamicmap_memoization(self.callback, self.streams):
            retval = self.callback(*args, **kwargs)
        return self._style(retval)