背景

由于一些安全上的要求，笔者所在公司在阿里云上的主机都要写白名单ACL。其中一个安全组中有监控的脚本需要发消息给企业微信，然后就犯了难——企业微信并没有接口告诉我们它的URL最后会解析为哪些ip，虽然确实有一个ip接口会给一个ip列表，但那个列表用在回调的情况下，和我们直接向企业微信发送HTTP请求时解析出来的ip并不一样

好在，我找到了这么个东西——企业微信域名IP列表​res.mail.qq.com

不过，这里面关于api接口所能解析出来的ip也多的让人眼花，一个个去配策略怕是配到死去了，于是就想用阿里云上的安全组策略的json模板，把这些ip填充进去生成个json文件，这样就可以直接导入策略了……

写出了Bug……

想法有了就开干。

写出来的代码是这样的——

import json

ips = '101.89.18.158,183.57.48.50,183.61.49.203,59.37.116.103,59.37.96.203,59.37.96.177,183.3.224.149,183.3.234.106,' \

'219.133.60.224,59.37.116.102,101.227.162.152,101.226.49.50,163.177.56.117,140.207.189.106,220.249.243.155,' \

'157.255.173.237,58.251.80.106,58.251.61.195,223.167.84.62,116.128.138.160,220.249.243.71,163.177.72.150,' \

'163.177.83.223,163.177.90.33,183.232.95.169,117.184.242.103,183.192.202.172,183.232.94.38,183.232.126.25,' \

'183.232.119.142,183.232.95.88,183.232.88.200,183.232.126.115,121.51.86.66,182.254.34.111,121.51.130.85,' \

'182.254.34.156,182.254.34.69,182.254.78.66,203.205.255.254,182.254.34.63,182.254.38.24,203.205.219.41,' \

'121.51.140.149,182.254.38.32,182.254.5.199,182.254.11.176'

ipslist = ips.split(",")

PolicyList = []

DictTemplate = {

"Policy": "Accept",

"Description": "访问微信接口",

"Priority": 1,

"NicType": "intranet",

"Direction": "egress",

"PortRange": "443/443",

"IpProtocol": "TCP",

"DestCidrIp": ""

}

for i in range(len(ipslist)):

DictTemplate["DestCidrIp"] = ipslist[i] + "/32"

PolicyList.append(DictTemplate)

print(json.dumps(PolicyList, ensure_ascii=False, indent=2))

当然，毫无疑问的，这个代码的运行是有问题的……

[

{

"Policy": "Accept",

"Description": "访问微信接口",

"Priority": 1,

"NicType": "intranet",

"Direction": "egress",

"PortRange": "443/443",

"IpProtocol": "TCP",

"DestCidrIp": "182.254.11.176/32"

},

{

"Policy": "Accept",

"Description": "访问微信接口",

"Priority": 1,

"NicType": "intranet",

"Direction": "egress",

"PortRange": "443/443",

"IpProtocol": "TCP",

"DestCidrIp": "182.254.11.176/32"

},

{

"Policy": "Accept",

"Description": "访问微信接口",

"Priority": 1,

"NicType": "intranet",

"Direction": "egress",

"PortRange": "443/443",

"IpProtocol": "TCP",

"DestCidrIp": "182.254.11.176/32"

},

......

]

"DestCidrIp" 的值是一样的……Why？

因为这里——

for i in range(len(ipslist)):

DictTemplate["DestCidrIp"] = ipslist[i] + "/32"

PolicyList.append(DictTemplate)

起初我以为，只要这样子，就可以把IP循环变成字典，然后插入到新的列表中，当然，实际上不行，因为我并非把某个值插入到了新的列表里，而是把整个字典对象放入了列表里，换言之，我的列表里实际的内容等于是——

[DictTemplate, DictTemplate, DictTemplate, DictTemplate, ......]

所以，每次循环，DictTemplate发生变化，列表里所有的元素都会变化……结果就是我输出的列表中的所有元素都一样，因为它们本来就是对应了同一个对象

当我操作一个列表的时候，我会用索引来访问值，而当我需要构建一个完整的字典的时候，我不可能只需要字典的值，字典里的键同样是我需要的东西，但是如果像上面这样做，结果就是我只是在重复的导入同一个对象，故而列表中充斥着同样的元素

修Bug……

知道了错在哪，问题就好解决了，Python的字典类型有个方法，copy()

for i in range(len(ipslist)):

DictTemplateCopy = DictTemplate.copy()

DictTemplateCopy["DestCidrIp"] = ipslist[i] + "/32"

PolicyList.append(DictTemplateCopy)

在操作字典对象之前，创建一个浅复制的对象，然后对这个对象进行操作并插入到列表中，再次循环的时候会再次创建另一个浅复制的对象，当然，之前那个对象就消失了

在交互式解释器里可以做这样一个实验

>>> DictTemplate = {

... "Policy": "Accept",

... "Description": "访问微信接口",

... "Priority": 1,

... "NicType": "intranet",

... "Direction": "egress",

... "PortRange": "443/443",

... "IpProtocol": "TCP",

... "DestCidrIp": ""

... }

>>>

>>> copy = DictTemplate.copy()

>>> print(id(copy))

2109669840920

>>> copy = DictTemplate.copy()

>>> print(id(copy))

2109670360392

>>> copy = DictTemplate.copy()

>>> print(id(copy))

2109669840920

>>> copy = DictTemplate.copy()

>>> print(id(copy))

2109670360392

不难看出，每次执行 copy = DictTemplate.copy() 后，打印其内存地址，该地址至少和上一次是不一样的。放在for循环里，就等于每次都是一个新的对象。

如此一来，执行结果就正常了——

[

{

"Policy": "Accept",

"Description": "访问微信接口",

"Priority": 1,

"NicType": "intranet",

"Direction": "egress",

"PortRange": "443/443",

"IpProtocol": "TCP",

"DestCidrIp": "101.89.18.158/32"

},

{

"Policy": "Accept",

"Description": "访问微信接口",

"Priority": 1,

"NicType": "intranet",

"Direction": "egress",

"PortRange": "443/443",

"IpProtocol": "TCP",

"DestCidrIp": "183.57.48.50/32"

},

{

"Policy": "Accept",

"Description": "访问微信接口",

"Priority": 1,

"NicType": "intranet",

"Direction": "egress",

"PortRange": "443/443",

"IpProtocol": "TCP",

"DestCidrIp": "183.61.49.203/32"

},

{

"Policy": "Accept",

"Description": "访问微信接口",

"Priority": 1,

"NicType": "intranet",

"Direction": "egress",

"PortRange": "443/443",

"IpProtocol": "TCP",

"DestCidrIp": "59.37.116.103/32"

},

{

"Policy": "Accept",

"Description": "访问微信接口",

"Priority": 1,

"NicType": "intranet",

"Direction": "egress",

"PortRange": "443/443",

"IpProtocol": "TCP",

"DestCidrIp": "59.37.96.203/32"

},

......

]

P.S. 日常写代码习惯于把功能都封装在模块里，模块之间变量隔离，因此就不会碰到这个情况。如果每次append的对象都是函数调用返回的结果，那么每次append进去的，一定是不同的对象。