vfs: add walk To eliminate "path prefix" (= "the root of vfs") part from "dirpath" yielded by "os.walk()" correctly, "path prefix" should have "os.sep" at the end of own string, but it isn't easy to ensure it, because: - examination by "path.endswith(os.sep)" isn't portable Some problematic encodings use 0x5c (= "os.sep" on Windows) as the tail byte of some multi-byte characters. - "os.path.join(path, '')" isn't portable With Python 2.7.9, this invocation doesn't add "os.sep" at the end of UNC path (see issue4557 for detail). Python 2.7.9 changed also behavior of "os.path.normpath()" (see *) and "os.path.splitdrive()" for UNC path. vfs root normpath splitdrive os.sep required =============== ============== =================== ============ z:\ z:\ z: + \ no z:\foo z:\foo z: + \foo yes z:\foo\ z:\foo z: + \foo yes [before Python 2.7.9] \\foo\bar \\foo\bar '' + \\foo\bar yes \\foo\bar\ \\foo\bar (*) '' + \\foo\bar yes \\foo\bar\baz \\foo\bar\baz '' + \\foo\bar\baz yes \\foo\bar\baz\ \\foo\bar\baz '' + \\foo\bar\baz yes [Python 2.7.9] \\foo\bar \\foo\bar \\foo\bar + '' yes \\foo\bar\ \\foo\bar\ (*) \\foo\bar + \ no \\foo\bar\baz \\foo\bar\baz \\foo\bar + \baz yes \\foo\bar\baz\ \\foo\bar\baz \\foo\bar + \baz yes If it is ensured that "normpath()"-ed vfs root is passed to "splitdrive()", adding "os.sep" is required only when "path" part of "splitdrive()" result isn't "os.sep" itself. This is just what "pathutil.nameasprefix()" examines. This patch applies "os.path.normpath()" on "self.join(None)" explicitly, because it isn't ensured that vfs root is already normalized: vfs itself is constructed with "realpath=False" (= avoid normalizing in "vfs.__init__()") in many code paths. This normalization should be much cheaper than subsequent file I/O for directory traversal.