07 · 异常、traceback 和调试

# tb_read.py —— 一个三层调用崩掉的样子
def load_batch(rows):
    return [to_score(r) for r in rows]


def to_score(row):
    return normalize(row["score"])


def normalize(v):
    return int(v) / 100


print(load_batch([{"score": "80"}, {"score": "n/a"}]))

Traceback (most recent call last):
  File "tb_read.py", line 14, in <module>
    print(load_batch([{"score": "80"}, {"score": "n/a"}]))
          ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "tb_read.py", line 3, in load_batch
    return [to_score(r) for r in rows]
            ~~~~~~~~^^^
  File "tb_read.py", line 7, in to_score
    return normalize(row["score"])
  File "tb_read.py", line 11, in normalize
    return int(v) / 100
           ~~~^^^
ValueError: invalid literal for int() with base 10: 'n/a'

# chain.py —— 同一个错误，三种转抛方式
import traceback


class ConfigError(Exception):
    pass


def read_port(raw, mode):
    try:
        return int(raw)
    except ValueError as e:
        if mode == "from":
            raise ConfigError("PORT 配置不是整数") from e        # ⭐ 显式串上
        if mode == "from_none":
            raise ConfigError("PORT 配置不是整数") from None     # ⚠️ 抹掉根因
        raise ConfigError("PORT 配置不是整数")                    # 隐式串上


for mode in ("from", "from_none", "bare"):
    print("=" * 12, mode)
    try:
        read_port("八千", mode)
    except ConfigError:
        print(traceback.format_exc().strip())

# bare_except.py —— 裸 except 会连 Ctrl-C 一起吞
def run(body, catcher):
    try:
        body()
    except catcher:
        print(f"  被 {catcher.__name__} 接住了")
    else:
        print("  没有异常")


def ctrl_c():
    raise KeyboardInterrupt


def sys_exit():
    raise SystemExit(1)


def normal():
    raise ValueError("一个普通业务错误")


for name, body in (("Ctrl-C", ctrl_c), ("sys.exit", sys_exit), ("普通错误", normal)):
    print(name, "→ except Exception:")
    try:
        run(body, Exception)
    except BaseException as e:
        print(f"  漏了出去：{type(e).__name__}")
    print(name, "→ except BaseException:")
    run(body, BaseException)

# 够用的三层，别再多了
class AppError(Exception): ...            # 兜底：所有自己抛的
class RetryableError(AppError): ...       # ⭐ 调用方看到它就重试
class FatalError(AppError): ...           # ⭐ 调用方看到它就放弃并上报

# finally_return.py —— finally 里的 return 会把异常整个吃掉
def bad():
    try:
        raise ValueError("真正的错误")
    finally:
        return "一切正常"          # 💀 异常被丢弃，函数正常返回


def good():
    try:
        raise ValueError("真正的错误")
    finally:
        print("  清理动作跑了")    # ✅ 只做清理，不 return


print("bad() =", bad())
try:
    good()
except ValueError as e:
    print("good() 抛出：", e)

# assert_o.py —— 同一份代码，加不加 -O 结果相反
import os
import subprocess
import sys
import tempfile

CHILD = "\n".join([
    "def add_user(age):",
    "    assert age >= 0, '年龄不能是负数'",
    "    return {'age': age}",
    "",
    "print('__debug__ =', __debug__)",
    "print(add_user(-5))",
])
script = os.path.join(tempfile.mkdtemp(), "child.py")
with open(script, "w", encoding="utf-8") as fh:
    fh.write(CHILD)

for flags in ([], ["-O"]):
    r = subprocess.run([sys.executable, *flags, script],
                       capture_output=True, text=True, encoding="utf-8")
    print(f"--- python {' '.join(flags) or '(无参数)'} child.py → 退出码 {r.returncode}")
    print((r.stdout + r.stderr).strip().splitlines()[-1])

# devmode.py —— 忘了关文件，默认一声不吭
import os
import subprocess
import sys
import tempfile

CHILD = "\n".join([
    "import tempfile, os",
    "path = os.path.join(tempfile.mkdtemp(), 't.txt')",
    "f = open(path, 'w', encoding='utf-8')",
    "f.write('忘了关')",
    "del f",
    "print('跑完了，没报任何错')",
])
script = os.path.join(tempfile.mkdtemp(), "leak.py")
with open(script, "w", encoding="utf-8") as fh:
    fh.write(CHILD)

for flags in ([], ["-X", "dev"]):
    r = subprocess.run([sys.executable, *flags, script],
                       capture_output=True, text=True, encoding="utf-8")
    print(f"--- python {' '.join(flags) or '(无参数)'} leak.py")
    print((r.stdout + r.stderr).strip() or "(无输出)")

# werror.py —— DeprecationWarning 平时只是一行字
import os
import subprocess
import sys
import tempfile

CHILD = "\n".join([
    "import warnings",
    "warnings.warn('这个参数下个版本要删', DeprecationWarning)",
    "print('照样跑完')",
])
script = os.path.join(tempfile.mkdtemp(), "warn.py")
with open(script, "w", encoding="utf-8") as fh:
    fh.write(CHILD)

for flags in ([], ["-W", "error::DeprecationWarning"]):
    r = subprocess.run([sys.executable, *flags, script],
                       capture_output=True, text=True, encoding="utf-8")
    print(f"--- python {' '.join(flags) or '(无参数)'} warn.py → 退出码 {r.returncode}")
    print((r.stdout + r.stderr).strip() or "(无输出)")

# bp_hook.py —— 把 breakpoint() 换成「打印我关心的几个变量」
import inspect
import sys


def dump(*names):
    f = inspect.currentframe().f_back
    shown = {k: v for k, v in f.f_locals.items() if k in names}
    print(f"  [{f.f_code.co_name}:{f.f_lineno}] {shown}")


sys.breakpointhook = dump          # ⭐ breakpoint() 从此变成 dump()


def score(rows):
    total = 0
    for i, r in enumerate(rows):
        total += r["v"]
        if r["v"] < 0:
            breakpoint("i", "r", "total")
    return total


print("结果 =", score([{"v": 3}, {"v": -1}, {"v": 5}]))

# bp_off.py —— PYTHONBREAKPOINT=0 让所有 breakpoint() 变成空操作
import os
import subprocess
import sys
import tempfile

CHILD = "\n".join(["x = 41", "breakpoint()", "print('跑完了，x =', x + 1)"])
script = os.path.join(tempfile.mkdtemp(), "bp.py")
with open(script, "w", encoding="utf-8") as fh:
    fh.write(CHILD)

env = dict(os.environ, PYTHONBREAKPOINT="0")
r = subprocess.run([sys.executable, script], capture_output=True, text=True,
                   encoding="utf-8", env=env)
print("PYTHONBREAKPOINT=0 →", (r.stdout + r.stderr).strip(), "| 退出码", r.returncode)