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