如何在运行时覆盖包中的内容？

Question

编辑:我正在运行Python2.7.3

我是贸易公司的网络工程师，我一直在黑非克立特 (网站上的版本是旧的，这是我一直在处理的版本)，目的是让它与Brocade的NETCONF实现一起工作。为了让它与我们的Brocade设备一起工作，我不得不做一些调整，但是我不得不把包分叉，对源代码本身做一些调整。这对我来说没有“干净”的感觉，所以我决定尝试“以正确的方式”做这件事，并覆盖包中存在的几件事情*；具体地说有三件事：

1. 一个名为build()的“静态方法”，它属于HelloHandler类，它本身是SessionListener的一个子类
2. RPC类的"._id“属性(最初的实现使用了uuid，Brocade boxes不太喜欢这一点，所以在我最初的调整中，我只是将它更改为一个从未改变过的静态值)。
3. 构建XML筛选属性的util函数的小调整

到目前为止，我已经将此代码保存在文件brcd_ncclient.py中。

#!/usr/bin/env python

# hack on XML element creation and create a subclass to override HelloHandler's
# build() method to format the XML in a way that the brocades actually like

from ncclient.xml_ import *
from ncclient.transport.session import HelloHandler
from ncclient.operations.rpc import RPC, RaiseMode
from ncclient.operations import util

# register brocade namespace and create functions to create proper xml for
# hello/capabilities exchange

BROCADE_1_0 = "http://brocade.com/ns/netconf/config/netiron-config/"
register_namespace('brcd', BROCADE_1_0)

brocade_new_ele = lambda tag, ns, attrs={}, **extra: ET.Element(qualify(tag, ns), attrs, **extra)

brocade_sub_ele = lambda parent, tag, ns, attrs={}, **extra: ET.SubElement(parent, qualify(tag, ns), attrs, **extra)

# subclass RPC to override self._id to change uuid-generated message-id's;
# Brocades seem to not be able to handle the really long id's
class BrcdRPC(RPC):
    def __init__(self, session, async=False, timeout=30, raise_mode=RaiseMode.NONE):
        self._id = "1"
        return super(BrcdRPC, self).self._id

class BrcdHelloHandler(HelloHandler):
    def __init__(self):
        return super(BrcdHelloHandler, self).__init__()

    @staticmethod
    def build(capabilities):
        hello = brocade_new_ele("hello", None, {'xmlns':"urn:ietf:params:xml:ns:netconf:base:1.0"})
        caps = brocade_sub_ele(hello, "capabilities", None)
        def fun(uri): brocade_sub_ele(caps, "capability", None).text = uri
        map(fun, capabilities)
        return to_xml(hello)
        #return super(BrcdHelloHandler, self).build() ???

# since there's no classes I'm assuming I can just override the function itself
# in ncclient.operations.util?
def build_filter(spec, capcheck=None):
    type = None
    if isinstance(spec, tuple):
        type, criteria = spec
        # brocades want the netconf prefix on subtree filter attribute
        rep = new_ele("filter", {'nc:type':type})
        if type == "xpath":
            rep.attrib["select"] = criteria
        elif type == "subtree":
            rep.append(to_ele(criteria))
        else:
            raise OperationError("Invalid filter type")
    else:
        rep = validated_element(spec, ("filter", qualify("filter")),
                                    attrs=("type",))
        # TODO set type var here, check if select attr present in case of xpath..
    if type == "xpath" and capcheck is not None:
        capcheck(":xpath")
    return rep

然后，在我的文件netconftest.py中：

#!/usr/bin/env python

from ncclient import manager
from brcd_ncclient import *

manager.logging.basicConfig(filename='ncclient.log', level=manager.logging.DEBUG)

# brocade server capabilities advertising as 1.1 compliant when they're really not
# this will stop ncclient from attempting 1.1 chunked netconf message transactions
manager.CAPABILITIES = ['urn:ietf:params:netconf:capability:writeable-running:1.0', 'urn:ietf:params:netconf:base:1.0']

# BROCADE_1_0 is the namespace defined for netiron configs in brcd_ncclient
# this maps to the 'brcd' prefix used in xml elements, ie subtree filter criteria
with manager.connect(host='hostname_or_ip', username='username', password='password') as m:
    # 'get' request with no filter - for brocades just shows 'show version' data
    c = m.get()
    print c
    # 'get-config' request with 'mpls-config' filter - if no filter is
    # supplied with 'get-config', brocade returns nothing
    netironcfg = brocade_new_ele('netiron-config', BROCADE_1_0)
    mplsconfig = brocade_sub_ele(netironcfg, 'mpls-config', BROCADE_1_0)
    filterstr = to_xml(netironcfg)
    c2 = m.get_config(source='running', filter=('subtree', filterstr))
    print c2
    # so far it only looks like the supported filters for 'get-config'
    # operations are: 'interface-config', 'vlan-config' and 'mpls-config'

每当我运行我的netconftest.py文件时，我都会得到超时错误，因为在日志文件ncclient.log中，我可以看到我的子类定义(即为hello更改XML的子类定义--静态方法build)被忽略了，而Brocade框不知道如何解释原始ncclient HelloHandler.build()方法生成的**。我还可以在生成的日志文件中看到，我试图覆盖的其他内容也被忽略了，比如消息id(静态值1)以及XML过滤器。

所以，我有点不知所措。我确实从我的研究中找到了这篇博客文章/模块，它似乎完全能做我想做的事情，但我真的希望能够通过手工来理解我做错了什么，而不是使用已经有人写成的模块作为借口，不用我自己来解决这个问题。

*可否有人向我解释一下，这是否“猴子修补”，其实是坏的？我在我的研究中看到，猴子的补丁是不可取的，但是这个答案和这个答案让我很困惑。对我来说，我想重写这些部分的愿望将阻止我不得不维护我自己的整个分叉。

**为了提供更多的上下文，这个ncclient.transport.session.HelloHandler.build()默认生成的XML，Brocade框似乎不喜欢：

<?xml version='1.0' encoding='UTF-8'?>
    <nc:hello xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
        <nc:capabilities>
            <nc:capability>urn:ietf:params:netconf:base:1.0</nc:capability>   
            <nc:capability>urn:ietf:params:netconf:capability:writeable-running:1.0</nc:capability>   
        </nc:capabilities>
    </nc:hello>

我所重写的build()方法的目的是将上面的XML转换为这个XML( Brocade喜欢这样做)：

<?xml version="1.0" encoding="UTF-8"?>
    <hello xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
        <capabilities>
            <capability>urn:ietf:params:netconf:base:1.0</capability>
            <capability>urn:ietf:params:netconf:capability:writeable-running:1.0</capability>
        </capabilities>
    </hello>

Answer 1

原来“元信息”不应该这么仓促地删除，因为当我不完全理解我想要问什么的时候，再一次很难找到我想要的答案。我真正想做的是在运行时中覆盖包中的内容。

下面是我将brcd_ncclient.py更改为(为简洁而删除的注释)的内容：

#!/usr/bin/env python

from ncclient import manager
from ncclient.xml_ import *

brcd_new_ele = lambda tag, ns, attrs={}, **extra: ET.Element(qualify(tag, ns), attrs, **extra)
brcd_sub_ele = lambda parent, tag, ns, attrs={}, **extra: ET.SubElement(parent, qualify(tag, ns), attrs, **extra)

BROCADE_1_0 = "http://brocade.com/ns/netconf/config/netiron-config/"
register_namespace('brcd', BROCADE_1_0)

@staticmethod
def brcd_build(capabilities):
    hello = brcd_new_ele("hello", None, {'xmlns':"urn:ietf:params:xml:ns:netconf:base:1.0"})
    caps = brcd_sub_ele(hello, "capabilities", None)
    def fun(uri): brcd_sub_ele(caps, "capability", None).text = uri
    map(fun, capabilities)
    return to_xml(hello)

def brcd_build_filter(spec, capcheck=None):
    type = None
    if isinstance(spec, tuple):
        type, criteria = spec
        # brocades want the netconf prefix on subtree filter attribute
        rep = new_ele("filter", {'nc:type':type})
        if type == "xpath":
            rep.attrib["select"] = criteria
        elif type == "subtree":
            rep.append(to_ele(criteria))
        else:
            raise OperationError("Invalid filter type")
    else:
        rep = validated_element(spec, ("filter", qualify("filter")),
                                attrs=("type",))
    if type == "xpath" and capcheck is not None:
        capcheck(":xpath")
    return rep

manager.transport.session.HelloHandler.build = brcd_build
manager.operations.util.build_filter = brcd_build_filter

然后在netconftest.py

#!/usr/bin/env python

from brcd_ncclient import *

manager.logging.basicConfig(filename='ncclient.log', level=manager.logging.DEBUG)

manager.CAPABILITIES = ['urn:ietf:params:netconf:capability:writeable-running:1.0', 'urn:ietf:params:netconf:base:1.0']

with manager.connect(host='host', username='user', password='password') as m:
    netironcfg = brcd_new_ele('netiron-config', BROCADE_1_0)
    mplsconfig = brcd_sub_ele(netironcfg, 'mpls-config', BROCADE_1_0)
    filterstr = to_xml(netironcfg)
    c2 = m.get_config(source='running', filter=('subtree', filterstr))
    print c2

这让我几乎到达了我想去的地方。我仍然需要编辑原始源代码来更改使用uuid1().urn生成的消息id，因为我还没有弄清楚或不知道如何在运行时发生__init__之前更改对象的属性(小鸡/鸡蛋问题？)；下面是ncclient/operations/rpc.py中的违规代码

class RPC(object):
    DEPENDS = []
    REPLY_CLS = RPCReply
    def __init__(self, session, async=False, timeout=30, raise_mode=RaiseMode.NONE):
        self._session = session
        try:
            for cap in self.DEPENDS:
                self._assert(cap)
        except AttributeError:
            pass
        self._async = async
        self._timeout = timeout
        self._raise_mode = raise_mode
        self._id = uuid1().urn # Keeps things simple instead of having a class attr with running ID that has to be locked

这个食谱在ActiveState上最终帮助我了解了我真正想做的事情，这是我的功劳。我最初发布的代码在技术上没有错误--如果我想要做的是分叉自己的代码并对其进行更改和/或维护它，这根本不是我想要做的，至少现在没有。

我将编辑我的问题标题，以更好地反映我原本想要的--如果其他人有更好或更干净的想法，我是完全开放的。