Python Class Variables
A Class variable in Python is a variable that is accessible via the class rather than via an individual instance of the class. It's a variable shared among the class as a whole. Other languages sometimes refer to these as static variables or static fields.
class AttributeClass(): x = 5 print(AttributeClass.x)
Class attributes are sort of equivalent to what are called "static fields" in other programming languages. Consider this code:
class MyClass(): classVariable = 7 print(MyClass.classVariable) # output is: 7
Notice we're not creating an object of type
MyClass. Instead, we're referring to
We can refer to class variables via class instances:
object = MyClass() print(object.classVariable) # output is again 7
We can change the class variable and it will be reflected in all instances
object = MyClass() MyClass.classVariable = 10 # change the value for the whole class print(object.classVariable) # output is now 10
What if we change the class variable by referring to an instance of the class instead of the class itself? In this case the class variable changes to start acting like an instance variable
object = MyClass() # Remember that classVariable is initially 7 object.classVariable = 5 # Let's change classVariable for an individual instance print(object.classVariable) # Output is 5. We're referring to the instance now print(MyClass.classVariable) # output is 7. We're referring to the shared class value
Class variable are very useful for handling values that should be shared by all instances of a class. Use with caution, though, because it can be very confusing when the class variable is used like an instance variable.