a_list += list2
list.extend() is an expression and can be embedded in larger expressions.
+= (augmented assignment) is a statement, and statements can never be embedded in expressions.
So you can do this:
doubled_extender = lambda l, it: l.extend(v for v in it for _ in range(2))
but you can't use
Last but not least, the Augmented Assignments feature was added to the language later than