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Overriding Properties in Subclasses

Darren Jones
Managing Attributes With Python's property() Darren Jones 03:35
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00:00 Overriding Properties in Subclasses. When you create Python classes that include properties and release them in a package or library, you should expect that your users do a wide variety of things with them.

00:14 One of these things could be subclassing them to customize their functionalities. In these cases, your users have to be careful and be aware of a subtle gotcha.

00:25 If you partially override a property, then you lose the non-overridden functionality. For example, suppose you are coding an Employee class to manage employee information in your company’s internal accounting system. You already have a class called Person, and you think about subclassing it to reuse its functionality.

01:01 Person has a .name attribute implemented as a property. The current implementation of .name doesn’t meet the requirement of returning the name in uppercase letters.

01:14 Here’s how you end up solving this. In Employee, you override .name to make sure that when you access the attribute, you get the employee name in uppercase.

02:03 Employee works as you need. It returns the name using uppercase letters. However, subsequent tests uncover an unexpected behavior. You may be wondering what’s happened. When you override an existing property from a parent class, you override the whole functionality of that property.

02:25 In this example, you reimplemented the getter method only. Because of that, .name lost the rest of the functionality from the base class. You don’t have a setter method any longer.

02:39 The idea is that if you ever need to override a property in a subclass, then you should provide all of the functionality you need in the new version of the property at hand.

02:56 With this code in place, you can now set the employee’s name without issue.

03:29 Now that you’ve completed the content of the course, in the next section, you’ll review what you’ve learned.

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