def __contains__(self, point):
if not isinstance(point, Point):<EOL><INDENT>point = Point(point)<EOL><DEDENT>if point.y not in self.canvas:<EOL><INDENT>return False<EOL><DEDENT>else:<EOL><INDENT>return point.x in self.canvas[point.y]<EOL><DEDENT>
Check if a point has a value.