[case testWalrus1]

from typing import Optional

def foo(x: int) -> Optional[int]:

if x < 0:

return None

return x

def test(x: int) -> str:

if (n := foo(x)) is not None:

return str(x)

else:

return "<fail>"

[file driver.py]

from native import test

assert test(10) == "10"

assert test(-1) == "<fail>"

[case testWalrus2]

from typing import Optional, Tuple, List

class Node:

def __init__(self, val: int, next: Optional['Node']) -> None:

self.val = val

self.next = next

def pairs(nobe: Optional[Node]) -> List[Tuple[int, int]]:

if nobe is None:

return []

l = []

while next := nobe.next:

l.append((nobe.val, next.val))

nobe = next

return l

def make(l: List[int]) -> Optional[Node]:

cur: Optional[Node] = None

for x in reversed(l):

cur = Node(x, cur)

return cur

[file driver.py]

from native import Node, make, pairs

assert pairs(make([1,2,3])) == [(1,2), (2,3)]

assert pairs(make([1])) == []

assert pairs(make([])) == []