Python says I have only two values and need three while there are already three values

Question

(_,contours,hierarchy)=cv2.findContours(yellow, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
ValueError: not enough values to unpack (expected 3, got 2)

The code here throws an error saying that I am missing the third value but it already has three values

yellow = 1.  
cv2.RETR_TREE = 2.  
cv2.CHAIN_APROX_SIMPLE = 3.  

and I don't know what to do.

I define yellow as

yellow = cv2.inRange(hsv, yellow_lower, yellow_upper)

and both yellow_lower and yellow_upper are defined...

Can anybody help? Thanks in advance

Answer 1

您相信将返回三个值（第一个值将被丢弃）：

_, contours, hierarchy = cv2.findContours(yellow, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

诊断告诉您只有两个返回。 因此，接受它们两者：

contours, hierarchy = cv2.findContours(yellow, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

您似乎正在使用主版本号为2的downrev cv2库。 在3.x版本中，签名被更改为将图像作为第三个返回值。