Python图片拼贴程序报错：Inappropriate argument value（类型正确）求助

我正在完成一门课程作业，需使用三张图片创建拼贴画。运行程序时出现错误提示：

Inappropriate argument value (of correct type). An error occurred attempting to pass an argument to a function. Please check line 26

疑惑的是，第26行代码写法与上方另一张图片的处理代码完全相同，但该行并未报错，希望得到问题排查帮助。以下是我的代码：

def createCollage():
  fileName1 = pickAFile()
  src1= makePicture(fileName1)
  print(src1)
  filename2= pickAFile()
  src2=makePicture(filename2)
  print(src2)
  filename3=pickAFile()
  src3=makePicture(filename3)
  print (src3)
  canvas=makeEmptyPicture(1300,1000)
  print canvas
  targetX=0
  for sourceX in range(0,getWidth(src3)):
    targetY=100
    for sourceY in range(0,getHeight(src3)):
      color=getColor(getPixel(src3,sourceX,sourceY))
      setColor(getPixel(canvas,targetX,targetY), color)
      targetY=targetY+1
    targetX=targetX+1
  targetX=650
  for sourceX in range(0,getWidth(src1)-100):
    targetY= 300
    for sourceY in range(0,getHeight(src1)-50):
      color=getColor(getPixel(src1,sourceX,sourceY))
      setColor(getPixel(canvas,targetX,targetY), color)
      targetY=targetY+1
    targetX=targetX+1
  targetX=600
  for sourceX in range(0,getWidth(src2)):
    targetY=430
    for sourceY in range(150,getHeight(src2)):
      color=getColor(getPixel(src2,sourceX,sourceY))
      setColor(getPixel(canvas,targetX,targetY), color)
      targetY=targetY+1
    targetX=targetX+1
  targetX=10
  for sourceX in range(20,getWidth(src2)-100):
    targetY=270
    for sourceY in range(0,getHeight(src2)-50):
      color=getColor(getPixel(src2,sourceX,sourceY))
      setColor(getPixel(canvas,targetX,targetY), color)
      targetY=targetY+1
    targetX=targetX+1
  targetX=50
  for sourceX in range(0,getWidth(src1)):
    targetY= 430
    for sourceY in range(120,getHeight(src1)):
      color=getColor(getPixel(src1,sourceX,sourceY))
      setColor(getPixel(canvas,targetX,targetY), color)
      targetY=targetY+1
    targetX=targetX+1
  show(src1)
  show(src2)
  show(src3)
  show(canvas)
  return canvas
  writePictureTo(canvas,("C:/Temp Python/CollagePic.png"))  
createCollage()

排查方向与解决建议 #

1. 画布坐标越界（最可能原因） #

第26行是处理src1的setColor调用，报错核心是targetX或targetY超出了画布canvas的有效坐标范围：

• 画布宽度1300，有效X坐标范围为0~1299；高度1000，有效Y坐标范围为0~999。
• 若getWidth(src1)-100数值过大，加上起始targetX=650后，最终targetX会超过1299；同理getHeight(src1)-50加上起始targetY=300后，可能超过999。

验证方法：在第22行前添加打印语句，查看关键数值：

print("src1宽度:", getWidth(src1), "最终targetX:", 650 + (getWidth(src1)-100))
print("src1高度:", getHeight(src1), "最终targetY:", 300 + (getHeight(src1)-50))
print("画布宽高:", getWidth(canvas), getHeight(canvas))

修复方法：修改循环范围，确保坐标不越界：

# 限制X方向不超出画布
max_sourceX = min(getWidth(src1)-100, getWidth(canvas) - targetX)
for sourceX in range(0, max_sourceX):
    targetY= 300
    # 限制Y方向不超出画布
    max_sourceY = min(getHeight(src1)-50, getHeight(canvas) - targetY)
    for sourceY in range(0, max_sourceY):
        color=getColor(getPixel(src1,sourceX,sourceY))
        setColor(getPixel(canvas,targetX,targetY), color)
        targetY=targetY+1
    targetX=targetX+1

2. 循环范围逻辑错误 #

如果src1宽度小于100，getWidth(src1)-100会得到负数，此时range(0, 负数)不会生成有效循环，可添加判断避免异常：

if getWidth(src1) >= 100 and getHeight(src1) >=50:
    targetX=650
    for sourceX in range(0,getWidth(src1)-100):
        # 原循环代码
else:
    print("src1尺寸过小，无法执行该段裁剪")

3. 额外bug：return语句位置错误 #

代码中return canvas在writePictureTo之前，会导致保存图片的代码永远不会执行，需调整顺序：

show(canvas)
writePictureTo(canvas, "C:/Temp Python/CollagePic.png")  
return canvas

内容的提问来源于stack exchange，提问作者M Agrippa