This bit bothered me slightly:

>But what if we put a mutable object into the immutable tuple? Well, modification works, but we also get a TypeError at the same time.

    tup = ([],)
    tup[0] += [1]

Of course that's an error. It's equivalent to:

    temp = tup[0]
    temp += [1]
    tup[0] = temp

But the given explanation is way too obtuse. This shouldn't be a mystery at all:

> If we try to extend the list via += "then the statement executes STORE_SUBSCR, which calls the C function PyObject_SetItem, which checks if the object supports item assignment. In our case the object is a tuple, so PyObject_SetItem throws the TypeError. Mystery solved."