python - 无法更改Python中全局变量的值

Question

这个问题已经有答案了:

Why isn't the 'global' keyword needed to access a global variable? (11 个回答)

已关闭 4 年前。

我有一个函数，我想计算它被调用的次数(并以该计数器值作为名称保存图像)。我创建了一个名为 counter 的全局函数。但如果我这样做counter = counter+1 。它说Unresolved reference 。我错过了什么吗？

这是代码:

import numpy as np
import cv2
counter = 0
def saveImage(img):
    counter = counter+1

    imgs = str(counter) + '.jpg'
    cv2.imwrite('images/'+imgs, img)

Answer 1

import numpy as np
import cv2
counter = 0
def saveImage(img):
    global counter  # to modify global variable, you need to explicitly declare so... 
    counter = counter+1

    imgs = str(counter) + '.jpg'
    cv2.imwrite('images/'+imgs, img)