Function relpath

Lib/ntpath.py:744–788

Return a relative version of a path

(path, start=None)

supports_unicode_filenames = True

def relpath(path, start=None):
    """Return a relative version of a path"""
    path = os.fspath(path)
    if not path:
        raise ValueError("no path specified")

    if isinstance(path, bytes):
        sep = b'\\'
        curdir = b'.'
        pardir = b'..'
    else:
        sep = '\\'
        curdir = '.'
        pardir = '..'

    if start is None:
        start = curdir
    else:
        start = os.fspath(start)

    try:
        start_abs = abspath(start)
        path_abs = abspath(path)
        start_drive, _, start_rest = splitroot(start_abs)
        path_drive, _, path_rest = splitroot(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 = start_rest.split(sep) if start_rest else []
        path_list = path_rest.split(sep) if path_rest else []
        # 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 sep.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 iterable of paths given as input.