0(1) element: null
1(2) element: PyForStatement
2(3,10) READ ACCESS: lines
3(4) element: PyTargetExpression: line
4(5) WRITE ACCESS: line
5(6) element: PyIfStatement
6(7,3,10) READ ACCESS: line
7(8) element: PyStatementList. Condition: line == '@':true
8(9) element: PyAssignmentStatement
9(3,10) WRITE ACCESS: head
10() element: null