Index: Lib/ntpath.py
===================================================================
--- Lib/ntpath.py	(revision 53961)
+++ Lib/ntpath.py	(working copy)
@@ -15,7 +15,8 @@
            "getatime","getctime", "islink","exists","lexists","isdir","isfile",
            "ismount","walk","expanduser","expandvars","normpath","abspath",
            "splitunc","curdir","pardir","sep","pathsep","defpath","altsep",
-           "extsep","devnull","realpath","supports_unicode_filenames"]
+           "extsep","devnull","realpath","supports_unicode_filenames",
+           "isrelative"]
 
 # strings representing various path-related bits and pieces
 curdir = '.'
@@ -45,46 +46,59 @@
 
 # Return whether a path is absolute.
 # Trivial in Posix, harder on the Mac or MS-DOS.
-# For DOS it is absolute if it starts with a slash or backslash (current
-# volume), or if a pathname after the volume letter and colon / UNC resource
-# starts with a slash or backslash.
+# On MS-DOS, paths cannot be divided into just 'relative' and 'absolute'.
+# There are actually 4 different types of path:
+#
+# 1) Completely relative, e.g. foo\bar
+# 2) Completely absolute, e.g. c:\foo\bar or \\server\share
+# 3) Halfbreeds with no drive, e.g. \foo\bar
+# 4) Halfbreeds relative to cwd on a drive, e.g. c:foo\bar
 
 def isabs(s):
-    """Test whether a path is absolute"""
-    s = splitdrive(s)[1]
-    return s != '' and s[:1] in '/\\'
+    """Test whether a path is absolute.
 
+    Note that, on Windows, this does not imply that the path is relative."""
+    return ((s[1:2] == ':' and s[2:3] in '/\\') or
+            (s[0:1] in '/\\' and s[1:2] in '/\\'))
 
+def isrelative(s):
+    """Return True iff the path is completely relative.
+
+    Note that, on Windows, this does not imply that the path is absolute."""
+    return s[1:2] != ':' and s[0:1] not in '/\\'
+
+
 # Join two (or more) paths.
 
 def join(a, *p):
-    """Join two or more pathname components, inserting "\\" as needed"""
+    """Join two or more pathname components, inserting "\\" as needed."""
     path = a
     for b in p:
-        b_wins = 0  # set to 1 iff b makes path irrelevant
-        if path == "":
-            b_wins = 1
-
-        elif isabs(b):
-            # This probably wipes out path so far.  However, it's more
-            # complicated if path begins with a drive letter:
+        if len(b) >= 2 and b[0] in '/\\' and b[1] in '/\\':
+            # Specifying a UNC.  This wipes out path so far.  E.g:
+            # join('anything', '//server/share') = '//server/share'
+            path = ''
+        elif os.path.splitdrive(b)[0]:
+            # Specifying a new drive.  This wipes out path so far.  E.g:
+            # join('c:', 'd:/') = 'd:/'
+            # join('c:/', 'd:/') = 'd:/'
+            # join('c:/', 'd:') = 'd:'
+            # join('c:', 'd:') = 'd:'
+            # join('/foo/', 'd:') = 'd:'
+            # join('foo/', 'd:') = 'd:'
+            path = ''
+        elif len(b) >= 1 and b[0] in '/\\':
+            # Adding a path relative to the root of a drive.
+            # Throw away everything apart from the drive spec (if present).
+            # E.g:
             #     1. join('c:', '/a') == 'c:/a'
             #     2. join('c:/', '/a') == 'c:/a'
-            # But
             #     3. join('c:/a', '/b') == '/b'
-            #     4. join('c:', 'd:/') = 'd:/'
-            #     5. join('c:/', 'd:/') = 'd:/'
-            if path[1:2] != ":" or b[1:2] == ":":
-                # Path doesn't start with a drive letter, or cases 4 and 5.
-                b_wins = 1
+            #     4. join('/a', '/b') == '/b'
+            #     5. join('foo', '/b') == '/b'
+            path = splitdrive(path)[0]
 
-            # Else path has a drive letter, and b doesn't but is absolute.
-            elif len(path) > 3 or (len(path) == 3 and
-                                   path[-1] not in "/\\"):
-                # case 3
-                b_wins = 1
-
-        if b_wins:
+        if path == '':
             path = b
         else:
             # Join, and ensure there's a separator.
Index: Lib/test/test_ntpath.py
===================================================================
--- Lib/test/test_ntpath.py	(revision 53961)
+++ Lib/test/test_ntpath.py	(working copy)
@@ -46,11 +46,43 @@
 tester('ntpath.split("c:/")', ('c:/', ''))
 tester('ntpath.split("//conky/mountpoint/")', ('//conky/mountpoint', ''))
 
+# Tests for isabs and isrelative:
+# 0) Old tests
 tester('ntpath.isabs("c:\\")', 1)
 tester('ntpath.isabs("\\\\conky\\mountpoint\\")', 1)
-tester('ntpath.isabs("\\foo")', 1)
-tester('ntpath.isabs("\\foo\\bar")', 1)
+tester('ntpath.isabs("\\foo")', 0) # CHANGED: Was 1
+tester('ntpath.isabs("\\foo\\bar")', 0) # CHANGED: Was 1
 
+#1) Completely relative, e.g. foo\bar
+tester('ntpath.isrelative("foo\\bar")', True)
+tester('ntpath.isrelative("foo/bar")', True)
+tester('ntpath.isabs("foo\\bar")', False)
+tester('ntpath.isabs("foo/bar")', False)
+
+#2) Completely absolute, e.g. c:\foo\bar ...
+tester('ntpath.isrelative("c:\\foo\\bar")', False)
+tester('ntpath.isrelative("c:/foo/bar")', False)
+tester('ntpath.isabs("c:\\foo\\bar")', True)
+tester('ntpath.isabs("c:/foo/bar")', True)
+
+# ... or \\server\share
+tester('ntpath.isrelative("\\\\server\\\\share")', False)
+tester('ntpath.isrelative("//server/share")', False)
+tester('ntpath.isabs("\\\\server\\\\share")', True)
+tester('ntpath.isabs("//server/share")', True)
+
+#3) Halfbreeds with no drive, e.g. \foo\bar
+tester('ntpath.isrelative("\\foo\\bar")', False)
+tester('ntpath.isrelative("/foo/bar")', False)
+tester('ntpath.isabs("\\foo\\bar")', False)
+tester('ntpath.isabs("/foo/bar")', False)
+
+#4) Halfbreeds relative to cwd on a drive, e.g. c:foo\bar
+tester('ntpath.isrelative("c:foo\\bar")', False)
+tester('ntpath.isrelative("c:foo/bar")', False)
+tester('ntpath.isabs("c:foo\\bar")', False)
+tester('ntpath.isabs("c:foo/bar")', False)
+
 tester('ntpath.commonprefix(["/home/swenson/spam", "/home/swen/spam"])',
        "/home/swen")
 tester('ntpath.commonprefix(["\\home\\swen\\spam", "\\home\\swen\\eggs"])',
@@ -58,6 +90,7 @@
 tester('ntpath.commonprefix(["/home/swen/spam", "/home/swen/spam"])',
        "/home/swen/spam")
 
+# Old join() tests
 tester('ntpath.join("")', '')
 tester('ntpath.join("", "", "")', '')
 tester('ntpath.join("a")', 'a')
@@ -77,7 +110,7 @@
 tester('ntpath.join("d:\\", "a", "b")', 'd:\\a\\b')
 tester("ntpath.join('c:', '/a')", 'c:/a')
 tester("ntpath.join('c:/', '/a')", 'c:/a')
-tester("ntpath.join('c:/a', '/b')", '/b')
+tester("ntpath.join('c:/a', '/b')", 'c:/b') # CHANGED: Was '/b')
 tester("ntpath.join('c:', 'd:/')", 'd:/')
 tester("ntpath.join('c:/', 'd:/')", 'd:/')
 tester("ntpath.join('c:/', 'd:/a/b')", 'd:/a/b')
@@ -92,6 +125,64 @@
 tester("ntpath.join('a\\', '')", 'a\\')
 tester("ntpath.join('a\\', '', '', '', '')", 'a\\')
 
+# New join() tests
+# A note on test strategy:  we take advantage of the fact that join
+# works internally on pairs of paths, so we mostly only test pairs.
+# (i.e. we expect r=join(a,b,c) to be identical to z=join(a,b) and
+# r=join(z,c), so we only have to test join(a,b) and join(z,c) to
+# cover this.  And there are a lot less interesting combinations
+# of 2 paths then there are combinations of 3 paths).
+#
+# Where possible we run each test twice, once with / and once with \\.
+#
+# Simple join
+tester('ntpath.join("foo", "bar")', "foo\\bar")
+tester('ntpath.join("c:", "bar")', "c:bar")
+tester('ntpath.join("c:\\", "bar")', "c:\\bar")
+tester('ntpath.join("c:/", "bar")', "c:/bar")
+# join where 2nd arg has a drive
+tester('ntpath.join("c:", "d:\\")', "d:\\")
+tester('ntpath.join("c:", "d:/")', "d:/")
+tester('ntpath.join("c:\\", "d:\\")', "d:\\")
+tester('ntpath.join("c:/", "d:/")', "d:/")
+tester('ntpath.join("c:\\", "d:")', "d:")
+tester('ntpath.join("c:/", "d:")', "d:")
+tester('ntpath.join("c:", "d:")', "d:")
+tester('ntpath.join("\\foo\\", "d:")', "d:")
+tester('ntpath.join("/foo/", "d:")', "d:")
+tester('ntpath.join("foo\\", "d:")', "d:")
+tester('ntpath.join("foo/", "d:")', "d:")
+# join where 2nd arg has a slash
+tester('ntpath.join("c:", "\\a")', "c:\\a")
+tester('ntpath.join("c:", "/a")', "c:/a")
+tester('ntpath.join("c:\\", "\\a")', "c:\\a")
+tester('ntpath.join("c:/", "/a")', "c:/a")
+tester('ntpath.join("c:\\a", "\\b")', "c:\\b")
+tester('ntpath.join("c:/a", "/b")', "c:/b")
+tester('ntpath.join("\\a", "\\b")', "\\b")
+tester('ntpath.join("/a", "/b")', "/b")
+tester('ntpath.join("foo", "\\b")', "\\b")
+tester('ntpath.join("foo", "/b")', "/b")
+# Join with a UNC
+tester('ntpath.join("anything", "\\\\server\\share")', "\\\\server\\share")
+tester('ntpath.join("anything", "//server/share")', "//server/share")
+tester('ntpath.join("\\\\server\\share", "filename")', "\\\\server\\share\\filename")
+tester('ntpath.join("//server/share", "filename")', "//server/share\\filename")
+# Join to make a UNC
+tester('ntpath.join("anything", "\\\\")', "\\\\")
+tester('ntpath.join("anything", "//")', "//")
+tester('ntpath.join("\\\\", "server")', "\\\\server")
+tester('ntpath.join("//", "server")', "//server")
+tester('ntpath.join("\\\\server", "share")', "\\\\server\\share")
+tester('ntpath.join("//server", "share")', "//server\\share")
+# Special case where 2nd arg is empty
+tester('ntpath.join("a\\", "")', "a\\")
+tester('ntpath.join("a", "")', "a\\")
+# Join more than 2 path components:
+tester('ntpath.join("foo", "bar", "baz")', "foo\\bar\\baz")
+tester('ntpath.join("1", "2", "3", "4", "5", "6", "7", "8", "9", "10")',
+       "1\\2\\3\\4\\5\\6\\7\\8\\9\\10")
+
 tester("ntpath.normpath('A//////././//.//B')", r'A\B')
 tester("ntpath.normpath('A/./B')", r'A\B')
 tester("ntpath.normpath('A/foo/../B')", r'A\B')
Index: Lib/macpath.py
===================================================================
--- Lib/macpath.py	(revision 53961)
+++ Lib/macpath.py	(working copy)
@@ -9,7 +9,7 @@
            "getatime","getctime", "islink","exists","lexists","isdir","isfile",
            "walk","expanduser","expandvars","normpath","abspath",
            "curdir","pardir","sep","pathsep","defpath","altsep","extsep",
-           "devnull","realpath","supports_unicode_filenames"]
+           "devnull","realpath","supports_unicode_filenames", "isrelative"]
 
 # strings representing various path-related bits and pieces
 curdir = ':'
@@ -36,7 +36,11 @@
 
     return ':' in s and s[0] != ':'
 
+def isrelative(s):
+    """Test whether a path is relative"""
+    return not isabs(s)
 
+
 def join(s, *p):
     path = s
     for t in p:
Index: Lib/posixpath.py
===================================================================
--- Lib/posixpath.py	(revision 53961)
+++ Lib/posixpath.py	(working copy)
@@ -20,7 +20,7 @@
            "ismount","walk","expanduser","expandvars","normpath","abspath",
            "samefile","sameopenfile","samestat",
            "curdir","pardir","sep","pathsep","defpath","altsep","extsep",
-           "devnull","realpath","supports_unicode_filenames"]
+           "devnull","realpath","supports_unicode_filenames", "isrelative"]
 
 # strings representing various path-related bits and pieces
 curdir = '.'
@@ -49,6 +49,9 @@
     """Test whether a path is absolute"""
     return s.startswith('/')
 
+def isrelative(s):
+    """Test whether a path is relative"""
+    return not isabs(s)
 
 # Join pathnames.
 # Ignore the previous parts if a part is absolute.
Index: Lib/os2emxpath.py
===================================================================
--- Lib/os2emxpath.py	(revision 53961)
+++ Lib/os2emxpath.py	(working copy)
@@ -9,14 +9,15 @@
 import stat
 from genericpath import *
 from ntpath import (expanduser, expandvars, isabs, islink, splitdrive,
-                    splitext, split, walk)
+                    splitext, split, walk, isrelative)
 
 __all__ = ["normcase","isabs","join","splitdrive","split","splitext",
            "basename","dirname","commonprefix","getsize","getmtime",
            "getatime","getctime", "islink","exists","lexists","isdir","isfile",
            "ismount","walk","expanduser","expandvars","normpath","abspath",
            "splitunc","curdir","pardir","sep","pathsep","defpath","altsep",
-           "extsep","devnull","realpath","supports_unicode_filenames"]
+           "extsep","devnull","realpath","supports_unicode_filenames",
+           "isrelative"]
 
 # strings representing various path-related bits and pieces
 curdir = '.'