详解在Python程序中解析并修改XML内容的方法

需求
在实际应用中，需要对xml配置文件进行实时修改，

1.增加、删除 某些节点

2.增加，删除，修改某个节点下的某些属性

3.增加，删除，修改某些节点的文本

使用xml文档

    <?xml version="1.0" encoding="UTF-8"?>
    <framework>
      <processers>
        <processer name="AProcesser" file="lib64/A.so"
          path="/tmp">
        </processer>
        <processer name="BProcesser" file="lib64/B.so" value="fordelete">
        </processer>
        <processer name="BProcesser" file="lib64/B.so2222222"/>

        <services>
          <service name="search" prefix="/bin/search?"
            output_formatter="OutPutFormatter:service_inc">

            <chain sequency="chain1"/>
            <chain sequency="chain2"></chain>
          </service>
          <service name="update" prefix="/bin/update?">
            <chain sequency="chain3" value="fordelete"/>
          </service>
        </services>
      </processers>
    </framework>

实现思想
使用ElementTree，先将文件读入，解析成树，之后，根据路径，可以定位到树的每个节点，再对节点进行修改，最后直接将其输出

实现代码

    #!/usr/bin/python
    # -*- coding=utf-8 -*-
    # author : wklken@yeah.net
    # date: 2012-05-25
    # version: 0.1

    from xml.etree.ElementTree import ElementTree,Element

    def read_xml(in_path):
      '''读取并解析xml文件
        in_path: xml路径
        return: ElementTree'''
      tree = ElementTree()
      tree.parse(in_path)
      return tree

    def write_xml(tree, out_path):
      '''将xml文件写出
        tree: xml树
        out_path: 写出路径'''
      tree.write(out_path, encoding="utf-8",xml_declaration=True)

    def if_match(node, kv_map):
      '''判断某个节点是否包含所有传入参数属性
        node: 节点
        kv_map: 属性及属性值组成的map'''
      for key in kv_map:
        if node.get(key) != kv_map.get(key):
          return False
      return True

    #---------------search -----
    def find_nodes(tree, path):
      '''查找某个路径匹配的所有节点
        tree: xml树
        path: 节点路径'''
      return tree.findall(path)

    def get_node_by_keyvalue(nodelist, kv_map):
      '''根据属性及属性值定位符合的节点，返回节点
        nodelist: 节点列表
        kv_map: 匹配属性及属性值map'''
      result_nodes = []
      for node in nodelist:
        if if_match(node, kv_map):
          result_nodes.append(node)
      return result_nodes

    #---------------change -----
    def change_node_properties(nodelist, kv_map, is_delete=False):
      '''修改/增加 /删除 节点的属性及属性值
        nodelist: 节点列表
        kv_map:属性及属性值map'''
      for node in nodelist:
        for key in kv_map:
          if is_delete:
            if key in node.attrib:
              del node.attrib[key]
          else:
            node.set(key, kv_map.get(key))

    def change_node_text(nodelist, text, is_add=False, is_delete=False):
      '''改变/增加/删除一个节点的文本
        nodelist:节点列表
        text : 更新后的文本'''
      for node in nodelist:
        if is_add:
          node.text += text
        elif is_delete:
          node.text = ""
        else:
          node.text = text

    def create_node(tag, property_map, content):
      '''新造一个节点
        tag:节点标签
        property_map:属性及属性值map
        content: 节点闭合标签里的文本内容
        return 新节点'''
      element = Element(tag, property_map)
      element.text = content
      return element

    def add_child_node(nodelist, element):
      '''给一个节点添加子节点
        nodelist: 节点列表
        element: 子节点'''
      for node in nodelist:
        node.append(element)

    def del_node_by_tagkeyvalue(nodelist, tag, kv_map):
      '''同过属性及属性值定位一个节点，并删除之
        nodelist: 父节点列表
        tag:子节点标签
        kv_map: 属性及属性值列表'''
      for parent_node in nodelist:
        children = parent_node.getchildren()
        for child in children:
          if child.tag == tag and if_match(child, kv_map):
            parent_node.remove(child)

    if __name__ == "__main__":
      #1. 读取xml文件
      tree = read_xml("./test.xml")

      #2. 属性修改
       #A. 找到父节点
      nodes = find_nodes(tree, "processers/processer")
       #B. 通过属性准确定位子节点
      result_nodes = get_node_by_keyvalue(nodes, {"name":"BProcesser"})
       #C. 修改节点属性
      change_node_properties(result_nodes, {"age": "1"})
       #D. 删除节点属性
      change_node_properties(result_nodes, {"value":""}, True)

      #3. 节点修改
       #A.新建节点
      a = create_node("person", {"age":"15","money":"200000"}, "this is the firest content")
       #B.插入到父节点之下
      add_child_node(result_nodes, a)

      #4. 删除节点
        #定位父节点
      del_parent_nodes = find_nodes(tree, "processers/services/service")
        #准确定位子节点并删除之
      target_del_node = del_node_by_tagkeyvalue(del_parent_nodes, "chain", {"sequency" : "chain1"})

      #5. 修改节点文本
        #定位节点
      text_nodes = get_node_by_keyvalue(find_nodes(tree, "processers/services/service/chain"), {"sequency":"chain3"})
      change_node_text(text_nodes, "new text")

      #6. 输出到结果文件
      write_xml(tree, "./out.xml")

修改后的结果

    <?xml version='1.0' encoding='utf-8'?>
    <framework>
      <processers>
        <processer file="lib64/A.so" name="AProcesser" path="/tmp">
        </processer>
        <processer age="1" file="lib64/B.so" name="BProcesser">
          <person age="15" money="200000">this is the firest content</person>
        </processer>
        <processer age="1" file="lib64/B.so2222222" name="BProcesser">
          <person age="15" money="200000">this is the firest content</person>
        </processer>

        <services>
          <service name="search" output_formatter="OutPutFormatter:service_inc"
            prefix="/bin/search?">

            <chain sequency="chain2" />
          </service>
          <service name="update" prefix="/bin/update?">
            <chain sequency="chain3" value="fordelete">new text</chain>
          </service>
        </services>
      </processers>
    </framework>