lis.py

from typing import List

def parseInt(input: str) -> List[int]:
    try:
        return [int(input)]
    except ValueError:
        return []

def findUser(code: int) -> List[dict]:
    users = {
        2012: {"id": 1, "code": 2012, "name": "yuzu"},
        3308: {"id": 2, "code": 3308, "name": "yui"}
    }
    user = users.get(code)
    if user:
        return [user]
    else:
       return []

def findItem(userId: int) -> List[dict]:
    items = {
        1: {"userId": 1, "name": "keyboard"}
    }
    item = items.get(userId)
    if item:
        return [item]
    else:
        return []

keybord = [item["name"]
    for code in parseInt("2012")
    for user in findUser(code)
    for item in findItem(user["id"])]

print(keybord)  # => ['keyboard']

what = [item["name"]
    for code in parseInt("WXYZ")  # <- 失敗する
    for user in findUser(code)
    for item in findItem(user["id"])]

print(what)  # => []

guitor = [item["name"]
    for code in parseInt("3308")
    for user in findUser(code)
    for item in findItem(user["id"])]  # <- 失敗する

print(guitor)  # => []