改了一个文件，重做哪几步

（RULES 里每个目标记着它的依赖和命令；stale(目标) 判它要不要重做：目标不存在、或任何一个依赖比它新、或依赖自己就要重做；plan(目标) 按依赖先、目标后的顺序列出要重做的目标。）

贯穿 n05 的构建规则（目标 ← 依赖：命令）：

dist/app.pyz ← build/app.py, build/lib.py : zipapp build -o dist/app.pyz
build/app.py ← src/app.py                  : cp src/app.py build/
build/lib.py ← src/lib.py, src/lib.cfg     : gen.py src/lib.py src/lib.cfg > build/lib.py

MTIME 是每个文件的修改时间（数越大越新）：src/app.py 10、src/lib.py 12、src/lib.cfg 5、build/app.py 11、build/lib.py 13、dist/app.pyz 14。

先按现在的时间看要不要重做，再把 src/lib.cfg 改一下（时间变成 20）看一次：

RULES = {
    "dist/app.pyz": (["build/app.py", "build/lib.py"], "zipapp build -o dist/app.pyz"),
    "build/app.py": (["src/app.py"], "cp src/app.py build/"),
    "build/lib.py": (["src/lib.py", "src/lib.cfg"], "gen.py src/lib.py src/lib.cfg > build/lib.py"),
}
MTIME = {"src/app.py": 10, "src/lib.py": 12, "src/lib.cfg": 5, "build/app.py": 11, "build/lib.py": 13, "dist/app.pyz": 14}


def stale(target):
    if target not in RULES:
        return False
    if target not in MTIME:
        return True
    for d in RULES[target][0]:
        if stale(d) or MTIME.get(d, 0) > MTIME[target]:
            return True
    return False


def plan(target, done=None):
    done = [] if done is None else done
    if target in RULES:
        for d in RULES[target][0]:
            plan(d, done)
        if stale(target) and target not in done:
            done.append(target)
    return done

before = plan("dist/app.pyz")
MTIME["src/lib.cfg"] = 20
after = plan("dist/app.pyz")
print(str(before) + "/" + ",".join(after) + "/" + str(stale("build/app.py")))