sequence

• mutable sequences:

• immutable sequences:

PySequence_Check

int
PySequence_Check(PyObject *s)
{
    if (PyDict_Check(s))
        return 0;
    return Py_TYPE(s)->tp_as_sequence &&
        Py_TYPE(s)->tp_as_sequence->sq_item != NULL;
}

We can see that if it is not a dict and if it has a method __getitem__, then it returns 1.