Python ValueError: not enough values to unpack (expected 3, got 2)

Question

我得到 python

代码

_, threshold = cv2.threshold(gray_roi, 3, 255, cv2.THRESH_BINARY_INV)
_, contours, _ = cv2.findContours(threshold, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
contours = sorted(contours, key=lambda x: cv2.contourArea(x), reverse=True)

错误（第 2 行）

Traceback (most recent call last):
  File "/Users/hissain/PycharmProjects/hello/hello.py", line 17, in <module>
    _, contours, _ = cv2.findContours(threshold, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
ValueError: not enough values to unpack (expected 3, got 2)

如何解决？

Answer 1

根据cv2.findContoursdocumentation，函数return只有2个值。您尝试解压 3.

从第二行删除第一个 _（不需要的值）以匹配文档中的签名。

_, threshold = cv2.threshold(gray_roi, 3, 255, cv2.THRESH_BINARY_INV)
contours, _ = cv2.findContours(threshold, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
contours = sorted(contours, key=lambda x: cv2.contourArea(x), reverse=True)

一般来说，当您收到此 Python 错误消息时：

ValueError: not enough values to unpack (expected x got y)

搜索您尝试解压 y 个元素的位置，并尝试通过解压 x 个元素来修复它。

Answer 2

请参考OpenCV参考：

https://docs.opencv.org/2.4/modules/imgproc/doc/structural_analysis_and_shape_descriptors.html?highlight=findcontours#cv2.findContours

findCounters returns（轮廓，层次），所以你的第二行应该是：

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

Python ValueError: not enough values to unpack (expected 3, got 2)

Python ValueError: not enough values to unpack (expected 3, got 2)

python

pycharm

opencover

iterable-unpacking

代码

错误（第 2 行）