The problem is in `urlunparse`. If you check the RFC 2396, it has the following regular expression:

     ^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?

where group 3 is the //netloc, and 4 is netloc substring, of an url http://netloc/foobar - and this is what Python should use to parse an URI using RFC 2396... but:

    >>> pat.fullmatch('////netloc').group(4)
    ''
    >>> pat.fullmatch('/relative').group(4)
    >>> 

Someone took the shortcut. no netloc is different from netloc being the empty string '', but 

    >>> urlparse('////netloc')
    ParseResult(scheme='', netloc='', path='//netloc', params='', query='', fragment='')
    >>> urlparse('/netloc')
    ParseResult(scheme='', netloc='', path='/netloc', params='', query='', fragment='')

In the latter parsing result netloc should be *None*. Unfortunately I believe it is too late to change this either way.