"""Day 2 · Block 5 · Pythonic 写法、迭代与类型注解（参考答案）
对照用：先自己把 exercises/day2/05_pythonic.py 写完再看这里。
用法：uv run python exercises/solutions/day2/05_pythonic.py
预测练习（先在纸上写出输出，再到 REPL 验证）：
>>> print([x * 2 for x in range(3)], {x % 3 for x in range(10)})
>>> print({w: len(w) for w in ["a", "bb"]})
>>> g = (x * x for x in range(3))
>>> print(next(g), next(g), next(g)) # 再 next(g) → StopIteration
>>> print(sorted(["b", "A", "c"]), sorted(["b", "A", "c"], key=str.lower))
>>> print(sorted([("a", 3), ("b", 1)], key=lambda t: t[1]))
>>> print(any(x > 5 for x in [1, 7]), all(x > 5 for x in [1, 7]))
"""
from collections.abc import Iterator
from typing import Any
# ---- 任务 1 ----
def squares_of_evens(nums: list[int]) -> list[int]:
"""偶数的平方（用列表推导式一行完成）。例：[1, 2, 3, 4] -> [4, 16]"""
return [x * x for x in nums if x % 2 == 0]
# ---- 任务 2 ----
def word_length_map(words: list[str]) -> dict[str, int]:
"""词 -> 词长的字典（用字典推导式）。
例：["hi", "hey"] -> {"hi": 2, "hey": 3}
"""
return {word: len(word) for word in words}
# ---- 任务 3 ----
def flatten(matrix: list[list[int]]) -> list[int]:
"""把二维列表拉平（用嵌套推导式一行完成）。
例：[[1, 2], [3], []] -> [1, 2, 3]
"""
return [x for row in matrix for x in row]
# ---- 任务 4 ----
def sort_by_score(
records: list[dict[str, Any]], reverse: bool = True
) -> list[dict[str, Any]]:
"""按 record["score"] 排序，返回新列表，不修改入参。
sorted 返回新列表，所以入参天然不会被改动（.sort() 才是原地）。
例：[{"n": "a", "score": 1}, {"n": "b", "score": 5}] -> b 在前
"""
return sorted(records, key=lambda r: r["score"], reverse=reverse)
# ---- 任务 5 ----
def all_passed(scores: list[int], threshold: int = 60) -> bool:
"""是否全部达到 threshold（用 all）。例：[60, 70] -> True"""
return all(score >= threshold for score in scores)
# ---- 任务 6 ----
def any_perfect(scores: list[int]) -> bool:
"""是否有满分 100（用 any）。例：[99, 100] -> True"""
return any(score == 100 for score in scores)
# ---- 任务 7 ----
def countdown(n: int) -> Iterator[int]:
"""生成器：依次 yield n, n-1, ..., 0。
例：list(countdown(3)) -> [3, 2, 1, 0]
"""
yield from range(n, -1, -1)
# ---- 任务 8 ----
def chunks(items: list[Any], size: int) -> Iterator[list[Any]]:
"""生成器：把 items 切成每段 size 个，最后一段可能不足。
size <= 0 时抛出 ValueError("size 必须为正")。
例：list(chunks([1, 2, 3, 4, 5], 2)) -> [[1, 2], [3, 4], [5]]
"""
if size <= 0:
raise ValueError("size 必须为正")
for start in range(0, len(items), size):
yield items[start : start + size]
# ---- 任务 9 ----
def even_sum_below(limit: int) -> int:
"""小于 limit 的偶数之和（用 sum(生成器表达式)）。例：10 -> 20"""
return sum(x for x in range(limit) if x % 2 == 0)
# ---- 任务 10 ----
def describe_command(cmd: str) -> str:
"""解析一条命令，必须用 match cmd.split(): 实现。
["add", a, b] -> f"结果：{int(a) + int(b)}"
["greet", name] -> f"你好，{name}"
["quit"] -> "再见"；[] -> "空命令"；其他 -> "未知命令"
例："add 3 4" -> "结果：7"
"""
match cmd.split():
case ["add", a, b]:
return f"结果：{int(a) + int(b)}"
case ["greet", name]:
return f"你好，{name}"
case ["quit"]:
return "再见"
case []:
return "空命令"
case _:
return "未知命令"
# ---- 任务 11 ----
def find_user(users: list[dict[str, Any]], name: str) -> dict[str, Any] | None:
"""按 name 查用户，找不到返回 None（可用 next(..., None)）。
例：find_user([{"name": "小明"}], "小刚") -> None
"""
return next((user for user in users if user.get("name") == name), None)
# ---- 任务 12 ----
def numbered(words: list[str]) -> list[tuple[int, str]]:
"""给每个词编号，从 1 开始（用 enumerate(start=1)）。
例：["a", "b"] -> [(1, "a"), (2, "b")]
"""
return list(enumerate(words, start=1))
# ====================== 自测：不要改动下面的代码 ======================
def _check_squares_of_evens() -> None:
assert squares_of_evens([1, 2, 3, 4]) == [4, 16], (
"squares_of_evens([1,2,3,4]) 应为 [4, 16]"
)
assert squares_of_evens([]) == [], "空列表应返回空列表"
def _check_word_length_map() -> None:
assert word_length_map(["hi", "hey"]) == {"hi": 2, "hey": 3}, (
'word_length_map(["hi","hey"]) 应为 {"hi": 2, "hey": 3}'
)
def _check_flatten() -> None:
assert flatten([[1, 2], [3], []]) == [1, 2, 3], (
"flatten([[1,2],[3],[]]) 应为 [1, 2, 3]"
)
def _check_sort_by_score() -> None:
data = [{"n": "a", "score": 1}, {"n": "b", "score": 5}]
got = sort_by_score(data)
assert [r["n"] for r in got] == ["b", "a"], "默认降序，b 应在前"
assert [r["n"] for r in sort_by_score(data, reverse=False)] == ["a", "b"], (
"reverse=False 时应升序"
)
assert [r["n"] for r in data] == ["a", "b"], "不能修改入参 records"
def _check_all_passed() -> None:
assert all_passed([60, 70]) is True, "[60, 70] 应为 True"
assert all_passed([59, 100]) is False, "[59, 100] 应为 False"
assert all_passed([]) is True, "空列表的 all 为 True"
def _check_any_perfect() -> None:
assert any_perfect([99, 100]) is True, "[99, 100] 应为 True"
assert any_perfect([99, 98]) is False, "[99, 98] 应为 False"
def _check_countdown() -> None:
assert list(countdown(3)) == [3, 2, 1, 0], "countdown(3) 应为 [3, 2, 1, 0]"
assert list(countdown(0)) == [0], "countdown(0) 应为 [0]"
def _check_chunks() -> None:
assert list(chunks([1, 2, 3, 4, 5], 2)) == [[1, 2], [3, 4], [5]], (
"chunks([1,2,3,4,5], 2) 应为 [[1,2],[3,4],[5]]"
)
try:
list(chunks([1, 2], 0))
except ValueError:
pass
else:
raise AssertionError("size <= 0 时应抛出 ValueError")
def _check_even_sum_below() -> None:
assert even_sum_below(10) == 20, "even_sum_below(10) 应为 20"
assert even_sum_below(1) == 0, "even_sum_below(1) 应为 0"
def _check_describe_command() -> None:
assert describe_command("add 3 4") == "结果：7", '"add 3 4" 应为 "结果：7"'
assert describe_command("greet 小明") == "你好，小明", "greet 分支不对"
assert describe_command("quit") == "再见", '"quit" 应为 "再见"'
assert describe_command("") == "空命令", '"" 应为 "空命令"'
assert describe_command("jump") == "未知命令", '"jump" 应为 "未知命令"'
def _check_find_user() -> None:
users = [{"name": "小明", "age": 15}, {"name": "小红", "age": 16}]
assert find_user(users, "小红") == {"name": "小红", "age": 16}, "应找到小红"
assert find_user(users, "小刚") is None, "找不到时应返回 None"
def _check_numbered() -> None:
assert numbered(["a", "b"]) == [(1, "a"), (2, "b")], "编号应从 1 开始"
assert numbered([]) == [], "空列表应返回空列表"
CHECKS = [
_check_squares_of_evens,
_check_word_length_map,
_check_flatten,
_check_sort_by_score,
_check_all_passed,
_check_any_perfect,
_check_countdown,
_check_chunks,
_check_even_sum_below,
_check_describe_command,
_check_find_user,
_check_numbered,
]
def _run_checks() -> None:
passed = 0
for check in CHECKS:
name = check.__name__.removeprefix("_check_")
try:
check()
except NotImplementedError:
print(f"[TODO] {name}: 还没实现")
except AssertionError as e:
print(f"[FAIL] {name}: {e}")
except Exception as e:
print(f"[ERROR] {name}: {type(e).__name__}: {e}")
else:
passed += 1
print(f"[OK] {name}")
total = len(CHECKS)
tail = "，本文件全部完成！" if passed == total else ""
print(f"\n{passed}/{total} 通过{tail}")
if __name__ == "__main__":
_run_checks()