python里的pygame接收方向键无反应

python小白做的2048小游戏，本来是用wasd，之后想改进成方向键控制，不过试了很多方法都不行。

K_LEFT下面的print（'ininin'）是为了测试有没有成功接收到方向键，不过一直无法成功。

有没有大佬帮忙看看哪里出了什么问题（代码如下）

import random
import pygame,sys,time
from pygame.locals import *

matix=[[0 for i in range(4)]for i in range(4)]
score = 0
flag=True
def display():
    print(' \033[1;31;42m 欢迎进入2048小游戏 \033[0m')
    print('\r'
          ' ———— ———— ———— ———— \n'
          '|%4s|%4s|%4s|%4s|\n'
          '|%4s|%4s|%4s|%4s|\n'
          '|%4s|%4s|%4s|%4s|\n'
          '|%4s|%4s|%4s|%4s|\n'
          ' ———— ———— ———— ———— '
          %(ifZero(matix[0][0]), ifZero(matix[0][1]),
            ifZero(matix[0][2]), ifZero(matix[0][3]),
            ifZero(matix[1][0]), ifZero(matix[1][1]),
            ifZero(matix[1][2]), ifZero(matix[1][3]),
            ifZero(matix[2][0]), ifZero(matix[2][1]),
            ifZero(matix[2][2]), ifZero(matix[2][3]),
            ifZero(matix[3][0]), ifZero(matix[3][1]),
            ifZero(matix[3][2]), ifZero(matix[3][3]))
            )
    print(' \033[1;31;47m 得分：%s \033[0m'%(score))

def ifZero(s):
    return s if s!=0 else ""

def init():
    initNumFlag=0
    while True:
        k=2 if random.randrange(0,10)>1 else 4
        s=divmod(random.randrange(0,16),4)
        if matix[s[0]][s[1]]==0:
            matix[s[0]][s[1]]=k
            initNumFlag+=1
            if initNumFlag==2:
                break
    display()

def moveLeft():  #向左移动
    global score
    for i in range(4):
        for j in range(3):
            for k in range(1+j,4):
                if matix[i][k]>0:
                    if matix[i][j] == 0:
                        matix[i][j] = matix[i][k]
                        matix[i][k] = 0
                    elif matix[i][j] == matix[i][k]:
                        matix[i][j] *= 2
                        score += matix[i][j]
                        matix[i][k] = 0
                    break
    addRandomNum()

def moveRight():  #向右移动
    global score
    for i in range(4):
        for j in range(3,0,-1):
            for k in range(j-1,-1,-1):
                if matix[i][k]>0:
                    if matix[i][j]==0:
                        if k>0 and matix[i][k]==matix[i][k-1]:
                            matix[i][k]*=2
                            score+=matix[i][k]   #将当前的数作为score加上
                            matix[i][k-1]=0
                        if k==2 and matix[i][k-1]==0 and matix[i][k]==matix[i][k-2]:
                            matix[i][k] *=2
                            score += matix[i][k]   #将当前的数作为score加上
                            matix[i][k-2] = 0
                        matix[i][j] = matix[i][k]
                        matix[i][k]=0
                    elif matix[i][j] == matix[i][k]:
                        matix[i][j]*=2
                        score+=matix[i][j]
                        matix[i][k]=0
                    break
    addRandomNum()

def moveDown():    #向下移动
    global score
    for i in range(4):
        for j in range(3, 0, -1):
            for k in range(j - 1, -1, -1):
                if matix[k][i] > 0:
                    if matix[j][i] == 0:
                        matix[j][i] = matix[k][i]
                        matix[k][i] = 0
                    elif matix[j][i] == matix[k][i]:
                        matix[j][i] *= 2
                        score += matix[j][i]
                        matix[k][i] = 0
                    break
    addRandomNum()

def moveUp():   #向上移动
    global score
    for i in range(4):
        for j in range(3):
            for k in range(j + 1, 4):
                if matix[k][i] > 0:
                    if matix[j][i] == 0:
                        matix[j][i] = matix[k][i]
                        matix[k][i] = 0
                    elif matix[k][i] == matix[j][i]:
                        matix[j][i] *= 2
                        score += matix[j][i]
                        matix[k][i] = 0
                    break
    addRandomNum()

def addRandomNum():   #移动后自动添加随机数2或者4
    check = checkOver()
    while check:
        k=2 if random.randrange(0,10)>1 else 4
        s=divmod(random.randrange(0,16),4)
        if matix[s[0]][s[1]] == 0:
            matix[s[0]][s[1]] = k
            break
    display()

def checkOver():
    check = False
    for i in range(4):
        for j in range(3):
            if matix[i][j]==0 or matix[i][j]==matix[i][j+1] or matix[j][i]==matix[j+1][i]:
                check = True
    return check

def main():
    init()
    global flag
    print(' \033[1;31;46m 方向键控制 退格键退出:\033[0m')
    while flag :
        str = pygame.key.get_pressed()
        if str[pygame.K_LEFT]:
            print('ininini')
            moveLeft()
            if not checkOver():
                print('游戏结束')
                flag = False
        elif str[pygame.K_DOWN]:
            moveDown()
            if not checkOver():
                print('游戏结束')
                flag = False
        elif str[pygame.K_UP]:
            moveUp()
            if not checkOver():
                print('游戏结束')
                flag = False
        elif str[pygame.K_RIGHT]:
            moveRight()
            if not checkOver():
                print('游戏结束')
                flag = False
        elif str[pygame.K_ESCAPE]:
            break
        else:
            continue

if __name__=='__main__':
    pygame.init()
    main()
    pygame.quit()

最后事件问题这么写：

for e in pygame.event.get():
    if event.type==pygame.QUIT:
        ...
    elif event.type==pygame.KEYDOWN:
...