It's not ENTIRELY obvious. For example, tup[0].extend([1]) would work fine, and the behaviour of __iadd__() seems like it should be the same as extend(). In fac

It's not ENTIRELY obvious. For example, tup[0].extend([1]) would work fine, and the behaviour of __iadd__() seems like it should be the same as extend(). In fact, the reference[1] has the following thing to say: > For instance, to execute the statement x += y, where x is an instance of a class that has an __iadd__() method, x.__iadd__(y) is called. However, this is patently not true, apparently: tup = ([],) tup[0].__iadd__([1]) # Works print tup tup = ([],) tup[0] += [1] # TypeError print tup [1] https://docs.python.org/2/reference/datamodel.html#emulating-numeric-types https://docs.python.org/2/reference/datamodel.html#emulating...