What is attribute and instance in python?
As an object-oriented language, Python provides two scopes for attributes: class attributes and instance attributes. Show Python class attributes are variables of a class that are shared between all of its instances. They differ from instance attributes in that instance attributes are owned by one specific instance of the class only, and are not shared between instances. While the instance attribute in Python has exactly the same characteristics and definition as the other object-oriented languages, the class attribute is always mistakingly considered to be the exact equivalent of the static attribute in Java or C++. To be accurate, class attributes in Python and static attributes in Java or C++ have a lot in common, however, they have behavioral differences that I will highlight in this article. Let's start with the basics:
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Notice that the class attribute can be accessed as a class property and as an instance property, however, accessing an instance attribute as a class property raises an Behind the ScenesBehind the scenes, it is a game of namespaces. If you have already read the Zen of Python, the last line states: "Namespaces are one honking great idea -- let's do more of those!" So what is a namespace? In Python, a namespace is a mapping between objects and names. To keep it simple, let's say it is a Python dictionary that has as a key to the name of the object and its value as a value. Different namespaces can coexist with the property while the names within them are independent. Python classes and objects have different namespaces, for our example, we have
When you access an attribute (instance or class attribute) as a property of an object using the dot convention, it searches first in the namespace of that object for that attribute name. If it is found, it returns the value, otherwise, it searches in the namespace of the class. If nothing is found there as well, it raises an If we find, in one class, both an instance attribute and a class attribute with the same name, the access to that name from your object will get you the value in the object namespace. Below a simplified version of the lookup function.
When you access an attribute as a class property, it searches directly in the class namespace for the name of that attribute. If it is found, it returns the value,
otherwise, it raises an Class Attributes Mutate to Be Instance AttributesYeah, it might seem weird, but they do! Let's consider the following scenario and then comment it together.
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The affectation added a new instance attribute to the object With immutable objects, this behavior is always the same. However, with mutable objects like lists, for example, it is not always the case, depending on how you modify your class attribute. Let's change our previous class to have a list as a class attribute.
We modify that list as a property of the object
When a mutable class attribute is modified by an object, it does not mutateto turn into an instance attribute for that object. It stays shared between all the objects of the class with the new elements appended to it. However, if you attach a new list to that attribute (
You can compare the namespaces by yourself as proof of the previous behavior. ConclusionPython class attributes may be useful in different cases, however, they must be used with caution in order to avoid unexpected behaviors. Opinions expressed by DZone contributors are their own. What is an attribute in Python?Attributes of a class are function objects that define corresponding methods of its instances. They are used to implement access controls of the classes. Attributes of a class can also be accessed using the following built-in methods and functions : getattr() – This function is used to access the attribute of object.
What is the difference between instance and attributes?The difference is that class attributes are shared by all instances. When you change the value of a class attribute, it will affect all instances that share the same exact value. The attribute of an instance on the other hand is unique to that instance.
What is instance in Python?Instance is an object that belongs to a class. For instance, list is a class in Python. When we create a list, we have an instance of the list class. In this article, I will focus on class and instance variables.
What is class object and attribute in Python?A class attribute is a variable that belongs to a certain class, and not a particular object. Every instance of this class shares the same variable. These attributes are usually defined outside the __init__ constructor. An instance/object attribute is a variable that belongs to one (and only one) object.
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