Index: Doc/library/urlparse.rst
===================================================================
--- Doc/library/urlparse.rst	(revision 64563)
+++ Doc/library/urlparse.rst	(working copy)
@@ -52,6 +52,23 @@
       >>> o.geturl()
       'http://www.cwi.nl:80/%7Eguido/Python.html'
 
+   If the scheme value is not specified, urlparse following the syntax
+   specifications from RFC 1808, expects the netloc value to start with '//',
+   Otherwise, it is not possible to distinguish between net_loc and path
+   component and would classify the indistinguishable component as path as in
+   a relative url.
+
+       >>> from urlparse import urlparse
+       >>> urlparse('//www.cwi.nl:80/%7Eguido/Python.html')
+       ParseResult(scheme='', netloc='www.cwi.nl:80', path='/%7Eguido/Python.html',
+                  params='', query='', fragment='')
+       >>> urlparse('www.cwi.nl:80/%7Eguido/Python.html')
+       ParseResult(scheme='', netloc='', path='www.cwi.nl:80/%7Eguido/Python.html',
+                  params='', query='', fragment='')
+       >>> urlparse('help/Python.html')
+       ParseResult(scheme='', netloc='', path='help/Python.html', params='',
+                  query='', fragment='')
+
    If the *default_scheme* argument is specified, it gives the default addressing
    scheme, to be used only if the URL does not specify one.  The default value for
    this argument is the empty string.
 
Index: Lib/test/test_urlparse.py
===================================================================
--- Lib/test/test_urlparse.py	(revision 64563)
+++ Lib/test/test_urlparse.py	(working copy)
@@ -320,7 +320,28 @@
         # Issue 1637: http://foo.com?query is legal
         self.assertEqual(urlparse.urlparse("http://example.com?blahblah=/foo"),
                          ('http', 'example.com', '', '', 'blahblah=/foo', ''))
+    def test_withoutscheme(self):
+        # Test urlparse without scheme
+        # Issue 754016: urlparse goes wrong with IP:port without scheme
+        # RFC 1808 specifies that netloc should start with //, urlparse expects
+        # the same, otherwise it classifies the portion of url as path.
+        self.assertEqual(urlparse.urlparse("path"), 
+                ('','','path','','',''))
+        self.assertEqual(urlparse.urlparse("//www.python.org:80"),
+                ('','www.python.org:80','','','',''))
+        self.assertEqual(urlparse.urlparse("http://www.python.org:80"),
+                ('http','www.python.org:80','','','',''))
 
+    def test_portseparator(self):
+        # Issue 754016 makes changes for port separator ':' from scheme separator
+        self.assertEqual(urlparse.urlparse("path:80"),
+                ('','','path:80','','',''))
+        self.assertEqual(urlparse.urlparse("http:"),('http','','','','',''))
+        self.assertEqual(urlparse.urlparse("https:"),('https','','','','',''))
+        self.assertEqual(urlparse.urlparse("http://www.python.org:80"),
+                ('http','www.python.org:80','','','',''))
+
+
 def test_main():
     test_support.run_unittest(UrlParseTestCase)
 
Index: Lib/urlparse.py
===================================================================
--- Lib/urlparse.py	(revision 64563)
+++ Lib/urlparse.py	(working copy)
@@ -158,11 +157,12 @@
             v = SplitResult(scheme, netloc, url, query, fragment)
             _parse_cache[key] = v
             return v
-        for c in url[:i]:
-            if c not in scheme_chars:
-                break
-        else:
-            scheme, url = url[:i].lower(), url[i+1:]
+        if (len(url) == i+1) or (not url[i+1].isdigit()):
+            for c in url[:i]:
+                if c not in scheme_chars:
+                    break
+            else:
+                scheme, url = url[:i].lower(), url[i+1:]
     if scheme in uses_netloc and url[:2] == '//':
         netloc, url = _splitnetloc(url, 2)
     if allow_fragments and scheme in uses_fragment and '#' in url: