Real Python: Getters and Setters: Manage Attributes in Python

If you come from a language like Java or C++, then you’re probably used to writing getter and setter methods for every attribute in your classes. These methods allow you to access and mutate private attributes while maintaining encapsulation. In Python, you’ll typically expose attributes as part of your public API and use properties when you need attributes with functional behavior.

Even though properties are the Pythonic way to go, they can have some practical drawbacks. Because of this, you’ll find some situations where getters and setters are preferable over properties.

In this tutorial, you’ll:

• Write getter and setter methods in your classes
• Replace getter and setter methods with properties
• Explore other tools to replace getter and setter methods in Python
• Decide when setter and getter methods can be the right tool for the job

To get the most out of this tutorial, you should be familiar with Python object-oriented programming. It’ll also be a plus if you have basic knowledge of Python properties and descriptors.

Getting to Know Getter and Setter Methods

When you define a class in object-oriented programming (OOP), you’ll likely end up with some instance and class attributes. These attributes are just variables that you can access through the instance, the class, or both.

Attributes hold the internal state of objects. In many cases, you’ll need to access and mutate this state, which involves accessing and mutating the attributes. Typically, you’ll have at least two ways to access and mutate attributes. You can either:

1. Access and mutate the attribute directly
2. Use methods to access and mutate the attribute

If you expose the attributes of a class to your users, then those attributes automatically become part of the class’s public API. They’ll be public attributes, which means that your users will directly access and mutate the attributes in their code.

Having an attribute that’s part of a class’s API will become a problem if you need to change the internal implementation of the attribute itself. A clear example of this issue is when you want to turn a stored attribute into a computed one. A stored attribute will immediately respond to access and mutation operations by just retrieving and storing data, while a computed attribute will run computations before such operations.

The problem with regular attributes is that they can’t have an internal implementation because they’re just variables. So, changing an attribute’s internal implementation will require converting the attribute into a method, which will probably break your users’ code. Why? Because they’ll have to change attribute access and mutation operations into method calls throughout their codebase if they want the code to continue working.

To deal with this kind of issue, some programming languages, like Java and C++, require you to provide methods for manipulating the attributes of your classes. These methods are commonly known as getter and setter methods. You can also find them referred to as accessor and mutator methods.

What Are Getter and Setter Methods?

Getter and setter methods are quite popular in many object-oriented programming languages. So, it’s pretty likely that you’ve heard about them already. As a rough definition, you can say that getters and setters are:

• Getter: A method that allows you to access an attribute in a given class
• Setter: A method that allows you to set or mutate the value of an attribute in a class

In OOP, the getter and setter pattern suggests that public attributes should be used only when you’re sure that no one will ever need to attach behavior to them. If an attribute is likely to change its internal implementation, then you should use getter and setter methods.

Implementing the getter and setter pattern requires:

1. Making your attributes non-public
2. Writing getter and setter methods for each attribute

For example, say that you need to write a Label class with text and font attributes. If you were to use getter and setter methods to manage these attributes, then you’d write the class like in the following code:

# label.pyclassLabel:def__init__(self,text,font):self._text=textself._font=fontdefget_text(self):returnself._textdefset_text(self,value):self._text=valuedefget_font(self):returnself._fontdefset_font(self,value):self._font=value

In this example, the constructor of Label takes two arguments, text and font. These arguments are stored in the ._text and ._font non-public instance attributes, respectively.

Then you define getter and setter methods for both attributes. Typically, getter methods return the target attribute’s value, while setter methods take a new value and assign it to the underlying attribute.