Book Image

The Python Apprentice

By : Robert Smallshire, Austin Bingham
Book Image

The Python Apprentice

By: Robert Smallshire, Austin Bingham

Overview of this book

Experienced programmers want to know how to enhance their craft and we want to help them start as apprentices with Python. We know that before mastering Python you need to learn the culture and the tools to become a productive member of any Python project. Our goal with this book is to give you a practical and thorough introduction to Python programming, providing you with the insight and technical craftsmanship you need to be a productive member of any Python project. Python is a big language, and it’s not our intention with this book to cover everything there is to know. We just want to make sure that you, as the developer, know the tools, basic idioms and of course the ins and outs of the language, the standard library and other modules to be able to jump into most projects.
Table of Contents (21 chapters)
Title Page
Credits
About the Authors
www.PacktPub.com
Customer Feedback
Preface
12
Afterword – Just the Beginning

Collaborating classes


The Law of Demeter is an object-oriented design principle that says you should never call methods on objects you receive from other calls. Or, put another way: Only talk to your immediate friends.

Figure 8.2: The Law of Demeter

We'll now modify our Flight class to accept an aircraft object when it is constructed, and we’ll follow the Law of Demeter by adding a method to report the aircraft model. This method will delegate to Aircraft on behalf of the client rather than allowing the client to "reach through" the Flight and interrogate the Aircraft object directly:

class Flight:
    """A flight with a particular passenger aircraft."""

    def __init__(self, number, aircraft):
        if not number[:2].isalpha():
            raise ValueError("No airline code in '{}'".format(number))

        if not number[:2].isupper():
           raise ValueError("Invalid airline code'{}'".format(number))

        if not (number[2:].isdigit() and int(number[2:]) <= 9999):
         ...