If we need to have stateful objects, we can add update methods that can change the Counter object. For example, we can introduce a method to add another value by delegating the work to the associated Counter. This switches the design pattern from a simple connection between computation and collection to a proper wrapper around the collection.
The method might look like this:
def add(self, value):
self.raw_counter[value] += 1
self.mean = self.compute_mean()
self.stddev = self.compute_stddev()
First, we've updated the state of the Counter. Then, we recomputed all of the derived values. This kind of processing might create tremendous computation overheads. There needs to be a compelling reason to recompute the mean and standard ...
