What is a mutator method? Explain why mutator methods usually return the value None.

Mutator method is used to modify the variable values. This method does not require to return any value. So, the return value of this method is none.

Explanation:

 a mutator method is a method used to control changes to a variable. They are also widely known as setter methods. Often a setter is accompanied by a getter (also known as an accessor), which returns the value of the private member variable.