def filePathDelta(origin, destination):
    """
    Return a list of strings that represent C{destination} as a path relative
    to C{origin}.

    It is assumed that both paths represent directories, not files. That is to
    say, the delta of L{twisted.python.filepath.FilePath} /foo/bar to
    L{twisted.python.filepath.FilePath} /foo/baz will be C{../baz},
    not C{baz}.

    @type origin: L{twisted.python.filepath.FilePath}
    @param origin: The origin of the relative path.

    @type destination: L{twisted.python.filepath.FilePath}
    @param destination: The destination of the relative path.
    """
    commonItems = 0
    path1 = origin.path.split(os.sep)
    path2 = destination.path.split(os.sep)
    for elem1, elem2 in zip(path1, path2):
        if elem1 == elem2:
            commonItems += 1
        else:
            break
    path = [".."] * (len(path1) - commonItems)
    return path + path2[commonItems:]

    Return a list of strings that represent C{destination} as a path relative
    to C{origin}.

    It is assumed that both paths represent directories, not files. That is to
    say, the delta of L{twisted.python.filepath.FilePath} /foo/bar to
    L{twisted.python.filepath.FilePath} /foo/baz will be C{../baz},
    not C{baz}.

    @type origin: L{twisted.python.filepath.FilePath}
    @param origin: The origin of the relative path.

    @type destination: L{twisted.python.filepath.FilePath}
    @param destination: The destination of the relative path.
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/_release.py