07 错误与空值 · Python 基础语法速通

01try / except / finally

Python

try:
    n = int("x")
except ValueError as e:
    print("bad", e)
finally:
    print("done")

Kotlin

try {
    val n = "x".toInt()
} catch (e: NumberFormatException) {
    println("bad $e")
} finally {
    println("done")
}

ArkTS

try {
  const n = Number.parseInt("x");
  if (Number.isNaN(n)) {
    throw new Error("bad");
  }
} catch (e) {
  console.info("bad", e);
} finally {
  console.info("done");
}

先捕获具体异常（如 ValueError），少写裸 except:。

02抛出

Python

def must_positive(n: int) -> int:
    if n <= 0:
        raise ValueError("n must be > 0")
    return n

Kotlin

fun mustPositive(n: Int): Int {
    require(n > 0) { "n must be > 0" }
    return n
}

ArkTS

function mustPositive(n: number): number {
  if (n <= 0) {
    throw new Error("n must be > 0");
  }
  return n;
}

03空值思维对照

Kotlin 的 ? / ArkTS 联合类型，在 Python 里变成显式 None 检查或早期返回。

Python

def len_or_zero(s: str | None) -> int:
    if s is None:
        return 0
    return len(s)

Kotlin

fun lenOrZero(s: String?): Int = s?.length ?: 0

ArkTS

function lenOrZero(s: string | null): number {
  return s?.length ?? 0;
}

04for/else、try/else

Python 特色：循环正常结束才走 else（被 break 则不走）。

Python

for x in [1, 2, 3]:
    if x == 9:
        break
else:
    print("not found")

Kotlin

// 无直接对应；用 flag 或 firstOrNull
val found = listOf(1, 2, 3).any { it == 9 }
if (!found) println("not found")

ArkTS

// 同样用标志位
let found = false;
for (const x of [1, 2, 3]) {
  if (x === 9) { found = true; break; }
}
if (!found) console.info("not found");