I'M getting an error in the following program on line 38 to a function call. The function is in the gameobjects module and the there's an error there as well on line 21. Here's the code.


background_image_filename = 'sushiplate.jpg'
sprite_image_filename = 'fugu.png'

import pygame
from pygame.locals import *
from sys import exit
from gameobjects import Vectory2


screen = pygame.display.set_mode((640, 480), 0, 32)
background = pygame.image.load(sprite_image_filename).convert_alpha()

clock = pygame.time.Clock()

sprite_pos = Vectory2(200, 150)
sprite_speed = 300.

while True:
    for event in pygame.event.get():
        if event.type == QUIT:
    pressed_key = pygame.key.get_pressed()
    key_direction = Vectory2(0, 0)
    if pressed_key[K_LEFT]:
        key_direction.x = -1
    elif pressed_key[K_RIGHT]:
        key_direction.x = + 1
    if pressed_key[K_UP]:
        key_direction.y = - 1
    elif pressed_key[K_DOWN]:
        key_direction.y = + 1
    screen.blit(background, (0,0))
    screen.blit(sprite, sprite_pos)
    time_passed = clock.tick(30)
    time_passed_seconds = time_passed / 1000.0
    sprite_pos += key_direction * sprite_speed * time_passed_seconds


import math

class Vectory2(object):
    def __init__(self, x = 0.0, y = 0.0):
        self.x = x
        self.y = y
    def __str__(self):
        return "(%s, %s)" % (self.x, self.y)
    def from_points(P1, P2):
        return Vectory2(P2[0] - P1[0], P2[1] - P1[1])
    def get_magnitude(self):
        return math.sqrt(self.x**2 + self.y**2)
    def normalize(self):
        magnitude = self.get_magnitude()
        self.x /= magnitude
        self.y /= magnitude
    # rhs stands for right hand side
    def __add__(self, rhs):
        return Vectory2(self.x + rhs.x, self.y + rhs.y)

Thanks for any and all help.

The only potential error that I see in line 21 in gameobjects.py is division by zero if x and y are both 0 in a Vectory2 instance. Why don't you post the exception traceback ? A bug in your code is that after the sequence with the keys in lines 29-36, the key_direction could very well be zero.

put in print or assert statements to get values of variables at point of error. You did not include image files to run your code.

ZeroDivisionError: float division
File "/home/developer/Projects/Beginning Game Development/Chapter 4/keymovement.py", line 38, in <module>
File "/home/developer/Projects/Beginning Game Development/Chapter 4/gameobjects.py", line 21, in normalize
self.x /= magnitude

The problem is that key_direction is (0,0) initially. You can't normalize the null vector. You could start with (1,0), or choose a random angle a in [0, 2*pi] and start with (cos(a), sin(a)).

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