Python subprocess的env为什么丢变量：继承、替换与单次覆盖

import json
import os
import subprocess
import sys
import tempfile

优化参数 = ["-" + "O" * sys.flags.optimize] if sys.flags.optimize else []
演示键 = ["DEMO_ENV_MODE", "DEMO_ENV_KEEP", "DEMO_ENV_EMPTY",
       "DEMO_ENV_RETRY", "DEMO_ENV_DEBUG"]
子代码 = ("import json, os; keys = " + repr(演示键)
       + "; print(json.dumps({k: os.environ.get(k) for k in keys}))")


def 测试父进程():
    # 仅修改独立测试父进程的虚构键，不改启动脚本的环境。
    os.environ.update(DEMO_ENV_MODE="parent", DEMO_ENV_KEEP="kept",
                      DEMO_ENV_EMPTY="")
    结果 = []
    基线 = {键: os.environ.get(键) for 键 in 演示键}
    缺省 = dict.fromkeys(演示键)

    def 记录(名称, 实际, 预期):
        if 实际 != 预期:
            raise RuntimeError("检查失败：" + 名称)
        结果.append({"检查": 名称, "通过": True, "观察": 实际})

    def 查看(环境):
        回执 = subprocess.run(
            [sys.executable, "-I", *优化参数, "-c", 子代码], env=环境,
            capture_output=True, text=True, check=True, timeout=10)
        return json.loads(回执.stdout)

    记录("默认继承", 查看(None), 基线)
    记录("单键映射替换", 查看({"DEMO_ENV_MODE": "once"}),
       {**缺省, "DEMO_ENV_MODE": "once"})
    副本 = os.environ.copy()
    副本["DEMO_ENV_MODE"] = "once"
    记录("复制后覆盖且父不变", [查看(副本), {
        键: os.environ.get(键) for 键 in 演示键}],
       [{**基线, "DEMO_ENV_MODE": "once"}, 基线])
    副本 = os.environ.copy()
    副本.pop("DEMO_ENV_KEEP", None)
    记录("删除只影响副本", [查看(副本), os.environ["DEMO_ENV_KEEP"]],
       [{**基线, "DEMO_ENV_KEEP": None}, "kept"])
    记录("空串不是缺失", 查看({"DEMO_ENV_EMPTY": ""}),
       {**缺省, "DEMO_ENV_EMPTY": ""})
    for 值 in (False, 3):
        try:
            查看({"DEMO_ENV_RETRY": 值})
        except TypeError:
            记录("拒绝非字符串：" + type(值).__name__, "TypeError", "TypeError")
        else:
            raise RuntimeError("非字符串未被拒绝")
    记录("显式转字符串", 查看({"DEMO_ENV_RETRY": str(3),
                           "DEMO_ENV_DEBUG": str(False)}),
       {**缺省, "DEMO_ENV_RETRY": "3", "DEMO_ENV_DEBUG": "False"})
    记录("空映射不继承演示键", 查看({}), 缺省)
    try:
        subprocess.run([sys.executable, "-I", *优化参数, "-c",
                        "raise SystemExit(7)"], env={}, check=True, timeout=10)
    except subprocess.CalledProcessError as 异常:
        记录("非零退出被check拒绝", 异常.returncode, 7)
    else:
        raise RuntimeError("非零退出未被拒绝")
    print(json.dumps({"独立检查数": len(结果), "结果": 结果}, ensure_ascii=False))


if __name__ == "__main__":
    if not sys.executable or not os.path.isabs(sys.executable):
        raise RuntimeError("本实验需要绝对路径解释器")
    if sys.argv[1:] == ["--demo-parent"]:
        测试父进程()
    else:
        with tempfile.TemporaryDirectory(prefix="env-demo-") as 临时目录:
            subprocess.run([sys.executable, "-I", *优化参数,
                            os.path.abspath(__file__), "--demo-parent"],
                           env={"DEMO_ENV_BOOT": "fictional"}, cwd=临时目录,
                           check=True, timeout=30)