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