从C/C++库中抑制stdout消息

我试图抑制用C实现的库打印到stdout的消息。

我的具体用例是OpenCV,所以我将在下面的MCVE中使用它。这个 estimateChessboardSharpness 当网格尺寸太小时(这种情况会发生),函数会打印输出 here ). 我做了一个 PR to fix it ,但与此同时,我想压制这条消息。例如

import cv2
import numpy as np

img = np.zeros((512, 640), dtype='uint8')
corners = []
for i in range(10):
    for j in range(8):
        corner = (30 + 3 * j, 70 + 3 * i)
        if i and j:
            corners.append(corner)
        if (i % 2) ^ (j % 2):
            img[corner[0]:corner[0] + 3, corner[1]:corner[1] + 3] = 255
corners = np.array(corners)

>>> cv2.estimateChessboardSharpness(img, (9, 7), corners)
calcEdgeSharpness: checkerboard too small for calculation.
((9999.0, 9999.0, 9999.0, 9999.0), None)

这条线似乎很简单 std::cout << ... ,所以我尝试了以下所有方法:

from contextlib import redirect_stdout
from os imoprt devnull
import sys

with redirect_stdout(None):
    cv2.estimateChessboardSharpness(img, (9, 7), corners)

with open(devnull, "w") as null, redirect_stdout(null):
    cv2.estimateChessboardSharpness(img, (9, 7), corners)

sys.stdout = open(devnull, "w")
cv2.estimateChessboardSharpness(img, (9, 7), corners)

我甚至试过 redirect_stderr 而不是 redirect_stdout 以防万一。我也试过设置 OPENCV_LOG_LEVEL=SILENT 在bash和 os.environ["OPENCV_LOG_LEVEL"] = "SILENT" 导入前在python中 cv2 ,我并没有预料到在这种情况下stdout会与日志记录混为一谈。

在所有情况下,消息都会打印出来。我该怎么让它停下来?