Python 的 sax 解析 xml 文件遇到了个错误，不知各位大佬有解决办法否？

a.xml：

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE dblp SYSTEM "dblp.dtd">
<article mdate="2017-05-28" key="journals/acta/Saxena96">
    <author>Sanjeev Saxena</author>
    <author>q</author>
    <author>w</author>
    <title>Parallel Integer Sorting and Simulation Amongst CRCW Models</title>
    <pages>607-619</pages>
    <year>1996</year>
    <volume>33</volume>
    <journal>Acta Inf</journal>
    <number>7</number>
    <url>db/journals/acta/acta33.html#Saxena96</url>
    <ee>htt</ee>
</article>

python 代码：

from xml.sax.handler import ContentHandler, EntityResolver
from xml.sax import parse
from itertools import combinations


class DBLP(ContentHandler, EntityResolver):
    passthrough = False
    paper_authors = []
    currTag = ''

    def startElement(self, name, attrs):
        if name == 'article':
            self.passthrough = True
        elif name == 'author' and self.passthrough:
            self.currTag = 'author'

    def endElement(self, name):
        if name == 'article':
            self.passthrough = False
            self.generate_paper_info()
            self.paper_authors = []
        elif name == 'author':
            self.currTag = ''

    def characters(self, chars):
        if self.passthrough and self.currTag == 'author':
            self.paper_authors.append(chars)

    def generate_paper_info(self):
        with open('dblp.txt', 'w') as f:
            if len(self.paper_authors) < 2:
                print 'Only one author'
            else:
                for info in combinations(self.paper_authors, 2):
                    f.write('{0} {1}\n'.format(info[0], info[1]))
                    print 'Write one piece of cooperation user'
                    
                    
 parse('a.xml', DBLP())

报错信息：

Traceback (most recent call last):
  File "dblp.py", line 40, in <module>
    parse('a.xml', DBLP())
  File "E:\Python2.7.12\lib\xml\sax\__init__.py", line 33, in parse
    parser.parse(source)
  File "E:\Python2.7.12\lib\xml\sax\expatreader.py", line 110, in parse
    xmlreader.IncrementalParser.parse(self, source)
  File "E:\Python2.7.12\lib\xml\sax\xmlreader.py", line 123, in parse
    self.feed(buffer)
  File "E:\Python2.7.12\lib\xml\sax\expatreader.py", line 213, in feed
    self._parser.Parse(data, isFinal)
  File "E:\Python2.7.12\lib\xml\sax\expatreader.py", line 397, in external_entity_ref
    "")
  File "E:\Python2.7.12\lib\xml\sax\saxutils.py", line 349, in prepare_input_source
    f = urllib.urlopen(source.getSystemId())
  File "E:\Python2.7.12\lib\urllib.py", line 87, in urlopen
    return opener.open(url)
  File "E:\Python2.7.12\lib\urllib.py", line 213, in open
    return getattr(self, name)(url)
  File "E:\Python2.7.12\lib\urllib.py", line 469, in open_file
    return self.open_local_file(url)
  File "E:\Python2.7.12\lib\urllib.py", line 483, in open_local_file
    raise IOError(e.errno, e.strerror, e.filename)
IOError: [Errno 2] : 'dblp.dtd'

分割线~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~·

<!DOCTYPE dblp SYSTEM "dblp.dtd">

只要把上面这句去掉就好了，想到用 EntityResolver 重写，忽略识别 dtd，但是不知道如何重写。