0(1) element: null
1(2) element: PyMatchStatement
2(3,8) refutable pattern: [x]
3(4,8) WRITE ACCESS: x
4(5) matched pattern: [x]
5(6) element: PyStatementList
6(7) element: PyExpressionStatement
7(9) READ ACCESS: y
8(9) ASSERTTYPE ACCESS: null
9(10) element: PyExpressionStatement
10(11) READ ACCESS: z
11() element: null