The Python cls Parameter

The cls parameter is used in a class method to gain access to the class to which the method belongs.

class MyClass:

    classVariable = 10

    # a class method
    @classmethod
    def myMethod(cls):
        return cls.classVariable


 MyClass.myMethod()    # Call the class method

Here, myMethod has cls as a parameter. When we call the class method myMethod, Python will pass the method's class as a paraneter to that method via the cls parameter. It's like calling MyClass.myMethod(MyClass) but we don't actually pass MyClass in. Python does it for us, and does it silently.

cls means "the class to which this method belongs", or "this" class. It's simliar to how the self parameter works.

Note

The name "cls" is just a convention. The first parameter of a class method will always be a reference to the class to which the method belongs, and by convention we use "cls". You're welcome to call it "thisClass" or whatever you fancy. You cannot call it class, though, since that's a reserved word. To make life easier for others it's best to stick to conventions and use "cls".