Book Image

Modern Python Cookbook - Second Edition

By : Steven F. Lott
Book Image

Modern Python Cookbook - Second Edition

By: Steven F. Lott

Overview of this book

Python is the preferred choice of developers, engineers, data scientists, and hobbyists everywhere. It is a great language that can power your applications and provide great speed, safety, and scalability. It can be used for simple scripting or sophisticated web applications. By exposing Python as a series of simple recipes, this book gives you insight into specific language features in a particular context. Having a tangible context helps make the language or a given standard library feature easier to understand. This book comes with 133 recipes on the latest version of Python 3.8. The recipes will benefit everyone, from beginners just starting out with Python to experts. You'll not only learn Python programming concepts but also how to build complex applications. The recipes will touch upon all necessary Python concepts related to data structures, object oriented programming, functional programming, and statistical programming. You will get acquainted with the nuances of Python syntax and how to effectively take advantage of it. By the end of this Python book, you will be equipped with knowledge of testing, web services, configuration, and application integration tips and tricks. You will be armed with the knowledge of how to create applications with flexible logging, powerful configuration, command-line options, automated unit tests, and good documentation.
Table of Contents (18 chapters)
Other Books You May Enjoy

Avoiding mutable default values for function parameters

In Chapter 3, Function Definitions, we looked at many aspects of Python function definitions. In the Designing functions with optional parameters recipe, we showed a recipe for handling optional parameters. At the time, we didn't dwell on the issue of providing a reference to a mutable structure as a default. We'll take a close look at the consequences of a mutable default value for a function parameter.

Getting ready

Let's imagine a function that either creates or updates a mutable Counter object. We'll call it gather_stats().

Ideally, a small data gathering function could look like this:

import collections
from random import randint, seed
from typing import Counter, Optional, Callable
def gather_stats_bad(
    n: int,
    samples: int = 1000,
    summary: Counter[int] = collections.Counter()
) -> Counter[int]:
        sum(randint(1, 6)
            for d in range...