Overall, this is a nice post. There are two quibbles though. 1). For the most part, "c = collections.Counter()" is almost always better than "c = defaultdict

Overall, this is a nice post. There are two quibbles though. 1). For the most part, "c = collections.Counter()" is almost always better than "c = defaultdict(int)" * Counter only supplies missing values rather than automatically inserting them upon lookup. * The Counter version is much clearer about what it is trying to do. The defaultdict version is cryptic to the uninitiated (understanding it entails knowing that it has a __missing__ method to insert values computed by a factory function and that int() with no arguments returns zero). * The Counter version provides helpful methods such as "most_common(n)". 2). An ellipsis in Python is normally used in a much different way than shown in the article (it's used for an extended slice notation in NumPy).