Chapter 2: Mutability and Object References
==============================================

.. code-block:: python

    # Chapter 2: Mutability and References

    print("IMMUTABLE OBJECT EXAMPLE (int):")

    a = 5
    b = a

    print("Before change:")
    print("a:", a, "id:", id(a))
    print("b:", b, "id:", id(b))

    # This creates a NEW integer object
    a = a + 1

    print("\nAfter change:")
    print("a:", a, "id:", id(a))
    print("b:", b, "id:", id(b))

    # ------------------------------------

    print("\nMUTABLE OBJECT EXAMPLE (list):")

    list1 = [1, 2, 3]
    list2 = list1  # Both reference the same object

    print("Before modification:")
    print("list1:", list1, "id:", id(list1))
    print("list2:", list2, "id:", id(list2))

    # This mutates the existing list object
    list1.append(4)

    print("\nAfter modification:")
    print("list1:", list1, "id:", id(list1))
    print("list2:", list2, "id:", id(list2))

    # ------------------------------------

    print("\nMAKING A REAL COPY:")

    list3 = list1.copy()  # Creates a new list object

    list1.append(5)

    print("list1:", list1, "id:", id(list1))
    print("list3:", list3, "id:", id(list3))