enter
f start: 10
coro yielded: 11
coro yielded: 12
f returned: 13
body start
f start: 30
coro yielded: 31
coro yielded: 32
body f returned: 33
body end
exit None None
f start: 20
coro yielded: 21
coro yielded: 22
f returned: 23
finished
