TypeError：對象不支持索引

Question

... 
return cls(P2[0] - P1[0], P2[1] - P1[1]) 
TypeError: 'Vector' object does not support indexing 

我是pygame和python的新手。我一直在努力練習建築類和向量，掙扎很多。

這裏是我的類文件

import math 

class Vector(object): 

    #defaults are set at 0.0 for x and y 
    def __init__(self, x=0.0, y=0.0): 
     self.x = x 
     self.y = y 

    #allows us to return a string for print 
    def __str__(self): 
     return "(%s, %s)"%(self.x, self.y) 

    # from_points generates a vector between 2 pairs of (x,y) coordinates 
    @classmethod 
    def from_points(cls, P1, P2): 
     return cls(P2[0] - P1[0], P2[1] - P1[1]) 

    #calculate magnitude(distance of the line from points a to points b 
    def get_magnitude(self): 
     return math.sqrt(self.x**2+self.y**2) 

    #normalizes the vector (divides it by a magnitude and finds the direction) 
    def normalize(self): 
     magnitude = self.get_magnitude() 
     self.x/= magnitude 
     self.y/= magnitude 

    #adds two vectors and returns the results(a new line from start of line ab to end of line bc) 
    def __add__(self, rhs): 
     return Vector(self.x +rhs.x, self.y+rhs.y) 

    #subtracts two vectors 
    def __sub__(self, rhs): 
     return Vector(self.x - rhs.x, self.y-rhs.y) 

    #negates or returns a vector back in the opposite direction 
    def __neg__(self): 
     return Vector(-self.x, -self.y) 

    #multiply the vector (scales its size) multiplying by negative reverses the direction 
    def __mul__(self, scalar): 
     return Vector(self.x*scalar, self.y*scalar) 

    #divides the vector (scales its size down) 
    def __div__(self, scalar): 
     return Vector(self.x/scalar, self.y/scalar) 

    #gives my vector class an ability to return a tuple 
    def tuple(self): 
     return (self.x, self.y) 

，這裏是我的程序代碼

#The simple mouse move game by Ramon Cabral 


#imports 
import pygame, sys, Vector 
from pygame.locals import * 
from Vector import * 

#game init 
pygame.init() 

#screen 
screen = pygame.display.set_mode((800,600),0,32) 

#images 
mouse_file = 'mouse.png' 
MOUSE = pygame.image.load(mouse_file).convert_alpha() 


#variables 
bgcolor = (255,255,255) 
position = Vector(100.0,100.0) 
heading = Vector() 

#clock and speed 
clock = pygame.time.Clock() 
speed = 250.0 


#main game function 
while True: 

    for event in pygame.event.get(): 
     if event.type == QUIT: 
      pygame.quit() 

     if event.type == MOUSEBUTTONDOWN: 
      destination = pygame.mouse.get_pos() 
      heading = Vector.from_points(position, destination) 
      heading.normalize() 

    screen.fill(bgcolor) 
    screen.blit(MOUSE, position.tuple()) 

    time_passed = clock.tick(30.) 
    time_passed_seconds = time_passed/1000.0 

    distance_moved = time_passed_seconds*speed 
    position += heading * distance_moved 
    pygame.display.update() 

Answer 1

它應該是：

@classmethod 
def from_points(cls, P1, P2): 
    return cls(P2.x - P1.x, P2.y - P1.y) 

的原因是因爲你的類沒有__getitem__方法所以你不能索引它：

P2[0] #not allowed since this calls `__getitem__` and your class doesn't define it.