def tikzline(x1, y1, x2, y2, modifier=""):
    """
    Return string for TikZ command to draw a line from (x1,y1) to (x2,y2), with optional `modifier` string to set draw style.
    """
    return f"\\draw{modifier} ({x1},{y1}) -- ({x2},{y2});" if not ((x1 == x2) and (y1 == y2)) else ""