are user defined classes mutable

Question

Say I want to create a class for car, tractor and boat. All these classes have an instance of engine and I want to keep t

Answer 1

EDIT: This is conceptually wrong, The immutable object in python can shed some light as to why.

class Engine():
    def __init__(self, sn):
        self.sn = sn

a = Engine(42)
b = a
print (a is b)

prints True.