proxy - python urllib2 can open localhost but not 127.0.0.1

Question

I am using python urllib2 library and can see a strange and nasty problem.

Windows 7.

My code:

import urllib2 as url_request


opener = url_request.build_opener(url_request.ProxyHandler({'http': 'http://login:password@server:8080'}))
request = url_request.Request("http://localhost");
response = opener.open(request)
print response.read()

It works perfectly well, but when I change localhost to 127.0.0.1 this error happens:

HTTPError: HTTP Error 502: Proxy Error ( Forefront TMG denied the specified Uniform Resource Locator (URL).  )

Another addresses like google.com can be opened sucessfully. The only problem is 127.0.0.1

Any ideas?

Answer 1

Set a no_proxy or NO_PROXY environment key with 127.0.0.1, optionally with localhost too:

import os

os.environ['no_proxy'] = '127.0.0.1,localhost'

On Windows the ProxyOverride key in the HKCUSoftwareMicrosoftWindowsCurrentVersionInternet Settings registry is consulted as well, you probably have localhost registered as exception. Check your proxy settings to verify this.