python - 导入 cv2 后，在 OSX 中使用 PyQT5 的 objc 奇怪警告

Question

在我使用 PyQt5 创建的一些简单的 GUI 应用程序中导入 cv2(否则没有警告)后，我在 OSX 中收到了这些客观的 c 警告。这是一些最小的示例(仅警告，没有导致错误):

版本:

PyQt5 5.10.1

PyQt5-sip 4.19.21

opencv-python 4.1.2.30

代码:

import sys
from PyQt5.QtWidgets import QWidget, QApplication, QDesktopWidget
import sqlite3
import cv2


class EmployeeBase(QWidget):
    def __init__(self, window_title, geometry):
        super().__init__()
        self.setGeometry(*geometry)
        self.setWindowTitle(window_title)
        win_rectangle = self.frameGeometry()
        center_point = QDesktopWidget().availableGeometry().center()
        win_rectangle.moveCenter(center_point)
        self.move(win_rectangle.topLeft())
        self.setStyleSheet('QPushButton:!hover {color: red}')
        self.show()


if __name__ == '__main__':
    connection = sqlite3.connect('Employees.db')
    cursor = connection.cursor()
    test = QApplication(sys.argv)
    window = EmployeeBase('Test', (0, 0, 500, 500))
    sys.exit(test.exec_())

结果:

objc[1741]: Class QCocoaPageLayoutDelegate is implemented in both /Users/emadboctor/Library/Python/3.7/lib/python/site-packages/cv2/.dylibs/QtGui (0x110fee5c0) and /usr/local/lib/python3.7/site-packages/PyQt5/Qt/lib/QtPrintSupport.framework/Versions/5/QtPrintSupport (0x119519f20). One of the two will be used. Which one is undefined.
objc[1741]: Class QCocoaPrintPanelDelegate is implemented in both /Users/emadboctor/Library/Python/3.7/lib/python/site-packages/cv2/.dylibs/QtGui (0x110fee638) and /usr/local/lib/python3.7/site-packages/PyQt5/Qt/lib/QtPrintSupport.framework/Versions/5/QtPrintSupport (0x119519f70). One of the two will be used. Which one is undefined.
objc[1741]: Class QCocoaApplicationDelegate is implemented in both /Users/emadboctor/Library/Python/3.7/lib/python/site-packages/cv2/.dylibs/QtGui (0x110fee340) and /usr/local/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqcocoa.dylib (0x1194b9480). One of the two will be used. Which one is undefined.
objc[1741]: Class QNSApplication is implemented in both /Users/emadboctor/Library/Python/3.7/lib/python/site-packages/cv2/.dylibs/QtGui (0x110fee2f0) and /usr/local/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqcocoa.dylib (0x1194b94d0). One of the two will be used. Which one is undefined.
objc[1741]: Class QCocoaMenuLoader is implemented in both /Users/emadboctor/Library/Python/3.7/lib/python/site-packages/cv2/.dylibs/QtGui (0x110fee2a0) and /usr/local/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqcocoa.dylib (0x1194b9570). One of the two will be used. Which one is undefined.
objc[1741]: Class QNSImageView is implemented in both /Users/emadboctor/Library/Python/3.7/lib/python/site-packages/cv2/.dylibs/QtGui (0x110fee660) and /usr/local/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqcocoa.dylib (0x1194b9660). One of the two will be used. Which one is undefined.
objc[1741]: Class QNSStatusItem is implemented in both /Users/emadboctor/Library/Python/3.7/lib/python/site-packages/cv2/.dylibs/QtGui (0x110fee6b0) and /usr/local/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqcocoa.dylib (0x1194b96b0). One of the two will be used. Which one is undefined.
objc[1741]: Class QNSOpenSavePanelDelegate is implemented in both /Users/emadboctor/Library/Python/3.7/lib/python/site-packages/cv2/.dylibs/QtGui (0x110fee480) and /usr/local/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqcocoa.dylib (0x1194b9750). One of the two will be used. Which one is undefined.

Answer 1

在 Python 上实现 Qt 和 OpenCV 的方式是通过绑定(bind)机制，其中可以从 Python 解释器调用共享 native 库中的元素(在这两种情况下都使用 C++ 编程)。这可以通过多种方式实现，例如 ctypes标准 Python 库的模块。

问题是当两个共享库公开相同的符号时。 OpenCV 可以使用 Qt 作为引擎来构建 GUI(它也可以使用其他的，但是您使用的版本被编译为包含 Qt 符号)。当解释器加载两个共享库(在本例中为 /Users/emadboctor/Library/Python/3.7/lib/python/site-packages/cv2/.dylibs/QtGui 和 /usr/local/lib/python3.7/site-packages/PyQt5/Qt/lib/QtPrintSupport.framework )时，它会发出警告，因为加载机制在不同位置检测到相同的符号。警告 One of the two will be used. Which one is undefined.意味着它可能需要一个或另一个，但没有预定义的顺序或任何偏好。如果您期望某些仅在两者之一中实现的行为(例如，Qt 的 cv2 库版本是 5.1 版，PyQt 库版本是 5.2，并且某个 doSomething 函数从一个版本到另一个版本。加载顺序将以不可预测的方式确定程序的行为)。

一般来说，由于您处于开发的早期阶段，并且 Qt 是一个相当稳定的库，您应该没问题。如果您遇到上述问题，您可以尝试不同的方法，例如重新编译 OpenCV 以使用您期望的 Qt 版本(或对 PyQt 执行相同操作)。我还建议您开始使用虚拟环境，从那时起，您还可以通过为不同项目使用不同版本的依赖项来缓解此问题。