Returns a tuple of old content and new content.

def get_contents(diff_part):
    """
    Returns a tuple of old content and new content.
    """
    old_sha = get_old_sha(diff_part)
    old_filename = get_old_filename(diff_part)
    old_contents = get_old_contents(old_sha, old_filename)
    new_filename = get_new_filename(diff_part)
    new_contents = get_new_contents(new_filename)
    return old_contents, new_contents