python自定义解析简单xml格式文件的方法

#!/usr/bin/env python
#encoding: utf-8
import re
class xmlparse:
  def __init__(self, xmlstr):
    self.xmlstr = xmlstr
    self.xmldom = self.__convet2utf8()
    self.xmlnodelist = []
    self.xpath = ''
  def __convet2utf8(self):
    headstr = self.__get_head()
    xmldomstr = self.xmlstr.replace(headstr, '')
    if 'gbk' in headstr: 
      xmldomstr = xmldomstr.decode('gbk').encode('utf-8')
    elif 'gb2312' in headstr:
      xmldomstr = self.xmlstr.decode('gb2312').encode('utf-8')
    return xmldomstr
  def __get_head(self):
    headpat = r'<\"1.0" encoding="utf-8" standalone="yes" ?><resultObject><a><product_id>aaaaa</product_id><product_name><![CDATA[bbbbb]]></a><b><product_id>bbbbb</product_id><product_name><![CDATA[bbbbb]]></b></product_name></resultObject>'
  xpath1 = '/product_id'
  xpath2 = '/product_id[1]'
  xpath3 = '/a/product_id'
  xp = xmlparse(xmlstr)
  print 'xmlstr:',xp.xmlstr
  print 'xmldom:',xp.xmldom
  print '------------------------------'
  getstr = xp.parse(xpath1)
  print 'xpath:',xp.xpath
  print 'get list:',xp.xmlnodelist
  print 'get string:', getstr
  print '------------------------------'
  getstr = xp.parse(xpath2)
  print 'xpath:',xp.xpath
  print 'get list:',xp.xmlnodelist
  print 'get string:', getstr
  print '------------------------------'
  getstr = xp.parse(xpath3)
  print 'xpath:',xp.xpath
  print 'get list:',xp.xmlnodelist
  print 'get string:', getstr

xmlstr: <"1.0" encoding="utf-8" standalone="yes" ?><resultObject><a><product_id>aaaaa</product_id><product_name><![CDATA[bbbbb]]></a><b><product_id>bbbbb</product_id><product_name><![CDATA[bbbbb]]></b></product_name></resultObject>
xmldom: <resultObject><a><product_id>aaaaa</product_id><product_name><![CDATA[bbbbb]]></a><b><product_id>bbbbb</product_id><product_name><![CDATA[bbbbb]]></b></product_name></resultObject>
------------------------------
xpath: /product_id
get list: ['aaaaa', 'bbbbb']
get string: aaaaa
------------------------------
xpath: /product_id[1] 
get list: ['aaaaa', 'bbbbb']
get string: bbbbb
------------------------------
xpath: /a/product_id
get list: ['aaaaa']
get string: aaaaa