如何绕过Python中urllib2的304错误

Question

首先，创建一个打开器，代码是 opener = urllib2.build_opener()。如果我想添加一个头信息：

request.add_header('if-modified-since', request.headers.get('last-nodified'))

我就会遇到一个错误代码：

Traceback (most recent call last):
  File "<pyshell#19>", line 1, in <module>
    feeddata = opener.open(request)
  File "C:\Python27\lib\urllib2.py", line 391, in open
    response = self._open(req, data)
  File "C:\Python27\lib\urllib2.py", line 409, in _open
    '_open', req)
  File "C:\Python27\lib\urllib2.py", line 369, in _call_chain
    result = func(*args)
  File "C:\Python27\lib\urllib2.py", line 1173, in http_open
    return self.do_open(httplib.HTTPConnection, req)
  File "C:\Python27\lib\urllib2.py", line 1142, in do_open
    h.request(req.get_method(), req.get_selector(), req.data, headers)
  File "C:\Python27\lib\httplib.py", line 946, in request
    self._send_request(method, url, body, headers)
  File "C:\Python27\lib\httplib.py", line 986, in _send_request
    self.putheader(hdr, value)
  File "C:\Python27\lib\httplib.py", line 924, in putheader
    str = '%s: %s' % (header, '\r\n\t'.join(values))
TypeError: sequence item 0: expected string, NoneType found

那我该怎么解决这个问题呢？

我尝试从 urllib2.BaseHandler 创建一个类，但没有成功。

Answer 1

你的错误信息显示：期望是字符串，但找到了NoneType。这让我猜测你把一个None值当作了头部信息。你真的写了'last-nodified'吗？你想要的头部信息可能是'last-modified'，不过即使是这样，你也应该检查一下它是否存在。如果request.headers.get()返回的是None，那就不要再把它当作头部信息使用了。