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'<?xml.*?>'
 headpatobj = re.compile(headpat)
 headregobj = headpatobj.match(self.xmlstr)
 if headregobj:
 headstr = headregobj.group()
 return headstr
 else:
 return ''
 def parse(self, xpath):
 self.xpath = xpath
 xpatlist = []
 xpatharr = self.xpath.split('/')
 for xnode in xpatharr:
 if xnode:
 spcindex = xnode.find('[')
 if spcindex > -1:
 index = int(xnode[spcindex+1:-1])
 xnode = xnode[:spcindex]
 else:
 index = 0;
 temppat = ('<%s>(.*?)' % (xnode, xnode),index)
 xpatlist.append(temppat)
 xmlnodestr = self.xmldom
 for xpat,index in xpatlist:
 xmlnodelist = re.findall(xpat,xmlnodestr)
 xmlnodestr = xmlnodelist[index]
 if xmlnodestr.startswith(r'aaaaabbbbb'
 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: <?xml version="1.0" encoding="utf-8" standalone="yes" ?>aaaaabbbbb
xmldom: aaaaabbbbb
------------------------------
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