ntpath.py 文件源码

def relpath(path, start=None):
    """Return a relative version of a path"""
    if isinstance(path, bytes):
        sep = b'\\'
        curdir = b'.'
        pardir = b'..'
    else:
        sep = '\\'
        curdir = '.'
        pardir = '..'

    if start is None:
        start = curdir

    if not path:
        raise ValueError("no path specified")

    try:
        start_abs = abspath(normpath(start))
        path_abs = abspath(normpath(path))
        start_drive, start_rest = splitdrive(start_abs)
        path_drive, path_rest = splitdrive(path_abs)
        if normcase(start_drive) != normcase(path_drive):
            raise ValueError("path is on mount %r, start on mount %r" % (
                path_drive, start_drive))

        start_list = [x for x in start_rest.split(sep) if x]
        path_list = [x for x in path_rest.split(sep) if x]
        # Work out how much of the filepath is shared by start and path.
        i = 0
        for e1, e2 in zip(start_list, path_list):
            if normcase(e1) != normcase(e2):
                break
            i += 1

        rel_list = [pardir] * (len(start_list)-i) + path_list[i:]
        if not rel_list:
            return curdir
        return join(*rel_list)
    except (TypeError, ValueError, AttributeError, BytesWarning, DeprecationWarning):
        genericpath._check_arg_types('relpath', path, start)
        raise


# Return the longest common sub-path of the sequence of paths given as input.
# The function is case-insensitive and 'separator-insensitive', i.e. if the
# only difference between two paths is the use of '\' versus '/' as separator,
# they are deemed to be equal.
#
# However, the returned path will have the standard '\' separator (even if the
# given paths had the alternative '/' separator) and will have the case of the
# first path given in the sequence. Additionally, any trailing separator is
# stripped from the returned path.