Book Image

Secret Recipes of the Python Ninja

Book Image

Secret Recipes of the Python Ninja

Overview of this book

This book covers the unexplored secrets of Python, delve into its depths, and uncover its mysteries. You’ll unearth secrets related to the implementation of the standard library, by looking at how modules actually work. You’ll understand the implementation of collections, decimals, and fraction modules. If you haven’t used decorators, coroutines, and generator functions much before, as you make your way through the recipes, you’ll learn what you’ve been missing out on. We’ll cover internal special methods in detail, so you understand what they are and how they can be used to improve the engineering decisions you make. Next, you’ll explore the CPython interpreter, which is a treasure trove of secret hacks that not many programmers are aware of. We’ll take you through the depths of the PyPy project, where you’ll come across several exciting ways that you can improve speed and concurrency. Finally, we’ll take time to explore the PEPs of the latest versions to discover some interesting hacks.
Table of Contents (17 chapters)
Title Page
Copyright and Credits
Packt Upsell
Foreword
Contributors
Preface
Index

Implementing Counters


The Counter collection is another dictionary-like object that counts hashable objects. Like dictionaries, Counters are unordered mappings of elements (stored as keys) and their respective quantities (stored as values). Value counts are stored as integer values, but can be any value, including zero and negative numbers.

Technically, Counter is a subclass of the dictionary class, so it has access to all the traditional dictionary methods. In addition, it has the following special methods available to it:

  • elements(): It returns an iterator object over the key elements, repeating each key until its quantity value is reached. Elements are printed in random order and, if an element's count is less than one, it will not be printed.

  • most_common([n]): It returns a list of the most common elements and their counts from most common to least. If n is provided, only that number of elements are returned, otherwise all elements are returned.

  • subtract([iterable or mapping]): It subtracts...