After I made my post How to Group and Count with Dictionaries I noticed there was something nice I could have added in. How to make a counter class that also remembers the order in which it first found something. It super easy to do in Python, see the following.
from collections import Counter, OrderedDict class OrderedCounter(Counter, OrderedDict): pass
This works because of the method resolution order. You can find out really easy what that is by trying
help(OrderedCounter) into the python console. I have reproduced what you would get for
""" Counter | Method resolution order: | Counter | __builtin__.dict | __builtin__.object OrderedCounter | Method resolution order: | OrderedCounter | collections.Counter | collections.OrderedDict | __builtin__.dict | __builtin__.object """
What has changed is that now
OrderedDict has been inserted in the order in which methods which be searched for when using
OrderedCounter just before
dict. So any of the dictionary methods will come
OrderedDict instead of
dict giving us the result we want.
This can be used on any class that inherits from
dict and you want to keep the order of its key as that in which they are inserted. And in the more general case it can be used to create a new class uses and alternative implementation of some interface.
For more information on this, there is a great post by Raymond Hettinger called Python’s super() considered super! that goes into all this in way more detail.