Exercises in .NET with Andras Nemes

Python language basics 74: validating class level properties

Introduction

In the previous post we discussed class level properties in some detail. The most important detail we learned is that there are only public members in a Python class. Properties can be added to “self” on the fly within the class but those properties will be visible to all external callers. So all you’ve learnt about access modifiers from your Java course, such as private or public is not applicable in Python.

In this post we’ll explore the basics of validating the values that are sent into the object initialiser. Validation is a large topic so consider this only as a light introduction.

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Python language basics 73: class level properties

Introduction

In the previous post we looked at initializers and class level properties. We saw how to add the init method to a class so that we could provide the name property. We also added a second init method so that we could still have an “empty” Person object with no preset name. We also discussed how to attach class level fields to “self” on the fly. The value assigned to those properties was available from another class level method.

In this post we’ll consider class level properties. I felt it was important to provide a post dedicated to that topic because the behaviour of class properties in Python is markedly different from other popular OOP languages such as Java, C#, C++ or VB.NET. At least I was quite surprised when I was first exposed to these class related details in Python.

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Python language basics 72: object initializers and class level properties

Introduction

We continued to explore the notion of classes in the previous post. We looked at the difference between constructors and initializers although we haven’t seen the initialisers in action yet. We also built our first class called Person that had one class method called shout. The shout method could be called on an instance of the Person class, i.e. a Person object using the standard dot notation.

In this post we’ll look at the role of initializers and how to supply method arguments to class methods.

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Python language basics 71: continuing with classes

Introduction

In the previous post we started discussing classes. We said that classes are the models for objects. The objects are instantiated based on the classes. A class describes the properties for the objects. E.g. a Car class can have a number of variables, such as colour, make, etc. A class can not only contain simple properties, but methods as well, as we’ll see later. Also, a class controls how an object can be instantiated.

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