Consider a list: list1 = [6,7,8,9] What is the difference between the following operations on list1:
list1 * 2
list1 * 2 uses the repetition operator to return a new list [6,7,8,9,6,7,8,9]. The original list1 remains unchanged as [6,7,8,9] since no assignment is made.
list1 *= 2
list1 *= 2 uses augmented assignment to modify list1 in-place. After execution, list1 becomes [6,7,8,9,6,7,8,9]. The same list object is modified.
list1 = list1 * 2
list1 = list1 * 2 creates a new list by repetition and assigns it to list1. The result is [6,7,8,9,6,7,8,9], but a new list object is created and list1 references this new object.
Explanation
The key difference is that operation (a) leaves list1 unchanged, while operations (b) and (c) both modify list1 to contain repeated elements. However, (b) modifies the existing list object in-place, whereas (c) creates a new list object and reassigns the variable. The textbook notes that after operations like concatenation, 'there is no change in ongoing lists' unless an assignment statement is used.