条件判断与循环

运维脚本的核心逻辑无非是：读数据 → 判断状态 → 执行动作。条件分支负责告警分级与异常处理，循环负责批量主机、多端口、多日志行的重复操作。

---

条件判断

cpu = 88
mem = 72
disk = 91

# 多条件组合
if disk >= 90:
    level = "CRITICAL"
elif cpu >= 85 or mem >= 85:
    level = "WARNING"
else:
    level = "OK"

print(f"告警级别: {level}")

成员测试与空值判断：

role = "web"
allowed_roles = {"web", "api", "worker"}

if role in allowed_roles:
    print(f"{role} 节点允许发布")

# 运维常见：空列表/None 表示无数据
failed_hosts = []
if not failed_hosts:
    print("全部主机巡检通过")

三元表达式（简单赋值）：

status = "up" if cpu < 80 else "degraded"

---

for 循环

hosts = [
    {"name": "web-01", "cpu": 45},
    {"name": "web-02", "cpu": 92},
    {"name": "db-01", "cpu": 60},
]

alerts = []
for h in hosts:
    if h["cpu"] >= 85:
        alerts.append(f"{h['name']} CPU={h['cpu']}%")

if alerts:
    print("告警列表:")
    for msg in alerts:
        print(f"  - {msg}")
else:
    print("无 CPU 告警")

range 用于重试次数：

MAX_RETRY = 3

for attempt in range(1, MAX_RETRY + 1):
    print(f"第 {attempt} 次连接尝试...")
    # 模拟：第 3 次成功
    if attempt == 3:
        print("连接成功")
        break
else:
    # 循环未被 break 打断时执行
    print("重试耗尽，连接失败")

---

while 循环

适合「直到条件满足才停止」的场景，务必避免死循环：

import time

wait_seconds = 0
timeout = 30
interval = 5

while wait_seconds < timeout:
    # 模拟：检查服务是否就绪
    service_ready = wait_seconds >= 10
    if service_ready:
        print(f"服务就绪，等待 {wait_seconds}s")
        break
    print(f"未就绪，{interval}s 后重试...")
    time.sleep(interval)  # 文档示例；实际脚本可用
    wait_seconds += interval
else:
    print(f"超时 {timeout}s，部署失败")

---

实战：端口探测逻辑

def check_ports(host: str, ports: list[int]) -> dict[int, str]:
    """模拟端口检测，返回 port -> 状态。"""
    # 假装 80/443 开放，其余关闭
    open_ports = {80, 443}
    result = {}
    for port in ports:
        if port in open_ports:
            result[port] = "open"
        else:
            result[port] = "closed"
    return result

target = "10.0.1.10"
ports = [22, 80, 443, 8080]
status_map = check_ports(target, ports)

for port, state in status_map.items():
    action = "记录" if state == "open" else "防火墙排查"
    print(f"{target}:{port} {state} -> {action}")

---

控制流速查

语句	用途
if / elif / else	告警分级、环境分支
for ... in ...	批量主机、遍历日志行
while	等待就绪、轮询状态
break	重试成功则退出
continue	跳过单台失败主机，继续下一台

---

小结

• 复杂条件拆成有意义的变量（如 level），避免嵌套过深
• 批量操作优先 for，轮询用 while 并设超时
• for/else 可表达「全部重试失败」的语义

下一章学习 函数，把巡检、告警、重试封装成可复用模块。