List insert at index that is well out of range - behaves like append

Question

I had a list

 a = [1, 2, 3]

when I did

a.insert(100, 100)

[1, 2, 3, 100]

as list was originally of siz

Answer 1

Perhaps the actual implementation will shed some light.

static int
ins1(PyListObject *self, Py_ssize_t where, PyObject *v)
{
    ...
    if (where > n)
        where = n;
    ...
}

So that answers the question of how.

Philosophically, lists are not arrays, and there are many list manipulations that are tolerant of weird indexing. For instance, l[1:1000] will return [2,3]. This is all meant as a convenience to the programmer.