How do I prevent Python's urllib(2) from following a redirect

Question

I am currently trying to log into a site using Python however the site seems to be sending a cookie and a redirect statement on the same page. Python seems to be following that redirect thus preventing me from reading the cookie send by the login page. How do I prevent Python's urllib (or urllib2) urlopen from following the redirect?

Answer 1

You could do a couple of things:

1. Build your own HTTPRedirectHandler that intercepts each redirect
2. Create an instance of HTTPCookieProcessor and install that opener so that you have access to the cookiejar.

This is a quick little thing that shows both

import urllib2

#redirect_handler = urllib2.HTTPRedirectHandler()

class MyHTTPRedirectHandler(urllib2.HTTPRedirectHandler):
    def http_error_302(self, req, fp, code, msg, headers):
        print "Cookie Manip Right Here"
        return urllib2.HTTPRedirectHandler.http_error_302(self, req, fp, code, msg, headers)

    http_error_301 = http_error_303 = http_error_307 = http_error_302

cookieprocessor = urllib2.HTTPCookieProcessor()

opener = urllib2.build_opener(MyHTTPRedirectHandler, cookieprocessor)
urllib2.install_opener(opener)

response =urllib2.urlopen("WHEREEVER")
print response.read()

print cookieprocessor.cookiejar

Answer 2

If all you need is stopping redirection, then there is a simple way to do it. For example I only want to get cookies and for a better performance I don't want to be redirected to any other page. Also I hope the code is kept as 3xx. let's use 302 for instance.

class MyHTTPErrorProcessor(urllib2.HTTPErrorProcessor):

    def http_response(self, request, response):
        code, msg, hdrs = response.code, response.msg, response.info()

        # only add this line to stop 302 redirection.
        if code == 302: return response

        if not (200 <= code < 300):
            response = self.parent.error(
                'http', request, response, code, msg, hdrs)
        return response

    https_response = http_response

cj = cookielib.CookieJar()
opener = urllib2.build_opener(urllib2.HTTPCookieProcessor(cj), MyHTTPErrorProcessor)

In this way, you don't even need to go into urllib2.HTTPRedirectHandler.http_error_302()

Yet more common case is that we simply want to stop redirection (as required):

class NoRedirection(urllib2.HTTPErrorProcessor):

    def http_response(self, request, response):
        return response

    https_response = http_response

And normally use it this way:

cj = cookielib.CookieJar()
opener = urllib2.build_opener(NoRedirection, urllib2.HTTPCookieProcessor(cj))
data = {}
response = opener.open('http://www.example.com', urllib.urlencode(data))
if response.code == 302:
    redirection_target = response.headers['Location']

Answer 3

urllib2.urlopen calls build_opener() which uses this list of handler classes:

handlers = [ProxyHandler, UnknownHandler, HTTPHandler,
HTTPDefaultErrorHandler, HTTPRedirectHandler,
FTPHandler, FileHandler, HTTPErrorProcessor]

You could try calling urllib2.build_opener(handlers) yourself with a list that omits HTTPRedirectHandler, then call the open() method on the result to open your URL. If you really dislike redirects, you could even call urllib2.install_opener(opener) to your own non-redirecting opener.

It sounds like your real problem is that urllib2 isn't doing cookies the way you'd like. See also How to use Python to login to a webpage and retrieve cookies for later usage?