0(1) element: null
1(2) element: PyAssertStatement
2(3) READ ACCESS: isinstance
3(4) READ ACCESS: s
4(5) READ ACCESS: basestring
5(6) element: PyCallExpression: isinstance
6(7) READ ACCESS: isinstance
7(8) READ ACCESS: x
8(9) READ ACCESS: int
9(10) element: PyCallExpression: isinstance
10(11) ASSERTTYPE ACCESS: s
11(12) ASSERTTYPE ACCESS: x
12() element: null