Book Image

Modern Python Standard Library Cookbook

By : Alessandro Molina
Book Image

Modern Python Standard Library Cookbook

By: Alessandro Molina

Overview of this book

The Python 3 Standard Library is a vast array of modules that you can use for developing various kinds of applications. It contains an exhaustive list of libraries, and this book will help you choose the best one to address specific programming problems in Python. The Modern Python Standard Library Cookbook begins with recipes on containers and data structures and guides you in performing effective text management in Python. You will find Python recipes for command-line operations, networking, filesystems and directories, and concurrent execution. You will learn about Python security essentials in Python and get to grips with various development tools for debugging, benchmarking, inspection, error reporting, and tracing. The book includes recipes to help you create graphical user interfaces for your application. You will learn to work with multimedia components and perform mathematical operations on date and time. The recipes will also show you how to deploy different searching and sorting algorithms on your data. By the end of the book, you will have acquired the skills needed to write clean code in Python and develop applications that meet your needs.
Table of Contents (21 chapters)
Title Page
Copyright and Credits
Packt Upsell
Contributors
Preface
Index

Operators to functions


Suppose you want to create a simple calculator. The first step is parsing the formula the user is going to write to be able to perform it. The basic formula is made of an operator and two operands, so you have, in practice, a function and its arguments.

But given +, -, and so on, how can we have our parser return the associated functions? Usually to sum two numbers, we just write n1 + n2, but we can't pass around + itself to be called with any n1 and n2.

This is because + is an operator and not a function, but underlying that it's still just a function in CPython that gets executed.

How to do it...

We can use the operator module to get a callable that represents any Python operator that we can store or pass around:

import operator

operators = {
    '+': operator.add,
    '-': operator.sub,
    '*': operator.mul,
    '/': operator.truediv
}

def calculate(expression):
    parts = expression.split()

    try:
        result = int(parts[0])
    except:
        raise ValueError...