[PyGame] object's movement to left leave shadow on the screen

[Zhaleh]

Hello everyone. I've wrote a simple code using pygame and I want my image to move right and left and after collision to wall change direction. The problem is that when I run it in movement to left it has some shadow! in screen. It does move but it leaves something like a shadow of itself on the screen. What would be the problem?

here is my code:

import pygame 
pygame.init()
screen=pygame.display.set_mode((800,600)) 

pygame.display.set_caption('visual rhythm')
icon=pygame.image.load("song.png")
pygame.display.set_icon(icon)

playerImg=pygame.image.load('spaceship.png')
playerX=370
playerY=400
def player(x,y):
    screen.blit(playerImg,(x,y))

running=True
while running:
    screen.fill((0,255,0))
    
    for event in pygame.event.get():
        if event.type==pygame.QUIT:
            running=False
    playerX+=0.2
    player(playerX,playerY)
    if playerX<=0:
        playerX+=0.2
        player(playerX,playerY)
    elif playerX>=746:
        while playerX>=0:
            playerX-=0.2
            player(playerX,playerY)
            pygame.display.update()
    pygame.display.update()