Python's Collections Module: OrderedCounter

What are we trying to achieve?

If you recall from last post, here's the Method Resolution Order of Counter class:
There's no way we can swap the priority order. One option is to be cheeky and make use of the __repr__ method of builtins.dict

Option1: Casting a Counter Object to dict

By casting the Counter to dict, print will use__repr__ method of dict which will make sure, order is maintained!

But this doesn't draw the idea home, I mean what if a novice looks at this code? He has no idea why we are casting the Counter to dict.
So a better approach would be to create our own custom Ordered_Counter class for clarity.

Option 2: Creating a custom OrderedCounter class

We can create a class that inherits from Counter and implement it's __repr__ method,

The idea is still the same: cast the Counter to dict but this time by providing abstraction and thereby improving the readability of code.

class OrderedCounter(Counter):    'Counter that remembers the order elements are first encountered'    def __repr__(self):                        # casting 'self' to dict will do the job        return '%s(%r)' % (self.__class__.__name__, dict(self))    def __reduce__(self):        return self.__class__, (dict(self),)

Here, the instantiation(creation) of OrderedCounter Object will be done by the __init__ method of Counter class.

The __reduce__ method implementaton is necessary for 'PICKLING' purpose which we will discuss in some other post.

OrderedCounter in action!

# creating Ordered Countersordered_c0 = OrderedCounter('kkkaaaajjjjkkaaakklll')ordered_c1 = OrderedCounter(["oranges", "apples", "apples", "bananas",                             "kiwis", "kiwis", "apples"])print(ordered_c0, ordered_c1, sep='
')"""OUTPUT => Order Maintained {'k': 7, 'a': 7, 'j': 4, 'l': 3}{'oranges': 1, 'apples': 3, 'bananas': 1, 'kiwis': 2}"""

There are some other ways too, but knowing these two ways are more than enough!

References:

https://stackoverflow.com/questions/35446015/creating-an-ordered-counter