问Python/Pygame为什么精灵不能移动？

EN

import pygame
from pygame.locals import *

import random

#----------------------------------------------------------------------

class Tokens(pygame.sprite.Sprite):

    def __init__(self, color, x, y, width, height):
        pygame.sprite.Sprite.__init__(self)

        self.image = pygame.Surface([width, height])
        self.image.fill(color)

        self.rect = self.image.get_rect(x=x, y=y)

#----------------------------------------------------------------------

# constants (uppercase names)

GRAY  = (220, 220, 220)
BLACK = (  0,   0,   0)
BLUE  = (  0,   0, 255)
RED   = (255,   0,   0)
WHITE = (255, 255, 255)

#----------------------------------------------------------------------

f = open("results", "a")
f.write("trial number, answer, reaction time, correct answer, number of balls in left circle at response, number of balls in middle circle at response, number of balls in right circle at response\n")
f.close()

g = 0

# initial x y coords for token 

x_coords = [265, 305, 345, 385, 425, 265, 305, 345, 385, 425, 265, 305, 345, 385, 425, 265, 305, 345, 385] 
y_coords = [170, 170, 170, 170, 170, 210, 210, 210, 210, 210, 250, 250, 250, 250, 250, 290, 290, 290, 290]

#----------------------------------------------------------------------

# start program

pygame.init()

screen = pygame.display.set_mode((720, 480))

clock = pygame.time.Clock()

state_reset = True

current_time = pygame.time.get_ticks()
end_time = current_time + 60*15*1000 # ms

# --- mainloop ---

while current_time < end_time:

    if state_reset:
        # chooses amount of tokens

        tokens_to_move = random.choice( (11,15,19) )

        tokens_left = 0
        tokens_right = 0

        # create tokens

        tokens_list = []
        tokens_group = pygame.sprite.Group()

        for i in range(tokens_to_move):
            token = Tokens((255,120,0), x_coords[i], y_coords[i], 20, 20)
            tokens_list.append( token )
            tokens_group.add( token )

        move_speed = 1000

        current_time = pygame.time.get_ticks()
        time_to_move = current_time + move_speed # ms

        selected_side = None

        state_selected = False
        state_reset = False


    # --- DRAWS ---

    screen.fill(GRAY)

    pygame.draw.rect(screen, BLACK, Rect((30,140), (200,200)))
    pygame.draw.rect(screen, BLACK, Rect((260,140), (200,200)))
    pygame.draw.rect(screen, BLACK, Rect((490,140), (200,200)))

    if state_selected:
        if selected_side == 'left':
            pygame.draw.rect(screen, BLUE, Rect((30,140), (200,200)))

        elif selected_side == 'right':
            pygame.draw.rect(screen, BLUE, Rect((490,140), (200,200)))

    tokens_group.draw(screen)

    pygame.display.update()

    # --- CHANGES ---

    if state_selected:
        if selected_time <= current_time:
            state_selected = False

    # moves token

    if tokens_to_move:
        if time_to_move <= current_time:
            time_to_move = current_time + move_speed
            tokens_to_move -= 1
            print 'tokens_to_move:', tokens_to_move
            if random.randint(1,2) == 1:
                tokens_list[tokens_to_move].rect.x -= 230
                tokens_left += 1
            else:
                tokens_list[tokens_to_move].rect.x += 230
                tokens_right += 1
    else:
        state_reset = True

    # --- EVENTS ---

    for event in pygame.event.get():
        if event.type == KEYDOWN:
            g += 1

            if event.key == K_ESCAPE:
                pygame.quit()
                exit()

            elif event.key == pygame.K_SPACE:
                print 'reset'
                state_reset = True

            if not selected_side:
                if event.key == K_LEFT:
                    answer = "left"
                    f = open("results", "a")
                    f.write(str(g) + ", left\n")
                    f.close()
                    selected_side = 'left'
                    print("You picked left!")
                    selected_time = current_time + 1000 # ms
                    move_speed = 0.1
                    state_selected = True

                elif event.key == K_RIGHT:
                    answer = "right"
                    f = open("results", "a")
                    f.write(str(g) + ", right\n")
                    f.close()
                    selected_side = 'right'
                    print("You picked right!")
                    selected_time = current_time + 1000 # ms
                    move_speed = 0.1
                    state_selected = True


    # --- CLOCK ---

    clock.tick(20) # 20 FPS 

    current_time = pygame.time.get_ticks()
    #print 'current_time:', current_time