为什么我在 macOS Catalina 下收到错误：Cannot run 'uic': “execvp: No such file or directory” for a PySide2 program？

Question

I want to execute a program which was written in python using PyQt5 and then migrated to PySide2 under MacOS Catalina. With PyQt5 it was executing fine. I have installed PySide2 like PyQt5:

python3 -m pip install PyQt5
python3 -m pip install PySide2

macOS was restarted afterwards.

Now, with PySide2 installed, I am getting an error in macOS when I am trying to load an Ui-file.

MRE which works under Linux, Windows and macOS Catalina:

#!/usr/bin/env python3

# Standard library imports
import sys

# Third party imports
from PySide2.QtCore import (QMetaObject,
                            Slot)
from PySide2.QtWidgets import (QApplication,
                               QWidget,                               
                               QPushButton,
                               QHBoxLayout,
                               QMessageBox)

def show_about():
    msg = QMessageBox()

    msg.setText("About this app.")
    msg.setStandardButtons(QMessageBox.Ok)

    msg.exec_()
    
class MainWindow(QWidget):    
    def __init__(self):        
        super().__init__()
        self.initUI()
        
    def initUI(self):        
        aboutButton = QPushButton("About")
        aboutButton.setObjectName("aboutButton")
        
        hbox = QHBoxLayout()
        hbox.addStretch(1)
        hbox.addWidget(aboutButton)        
        
        self.setLayout(hbox)
        
        QMetaObject.connectSlotsByName(self)
                
        self.setWindowTitle('Buttons')        
            
    @Slot()
    def on_aboutButton_clicked(self):
        show_about()
        
def main():    
    app = QApplication(sys.argv)
    win = MainWindow()
    win.show()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

MRE which fails under macOS Catalina, but works in Linux and Windows:

#!/usr/bin/env python3

# Standard library imports
import sys

# Third party imports
from PySide2.QtWidgets import (QApplication,
                               QMainWindow)

from PySide2.QtUiTools import loadUiType
   
class MainWindow(QMainWindow, loadUiType("win_main.ui")[0]):    
    def __init__(self):        
        super().__init__()
        self.setupUi(self)


def main():
    app = QApplication(sys.argv)
    win = MainWindow()
    win.show()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

Error:

Python 3.8.5 (/usr/local/bin/python3)
>>> %Run pyside2_win_main.py
Cannot run 'uic':  "execvp: No such file or directory"  -  Exit status  QProcess::NormalExit  ( 255 )
 Check if 'uic' is in PATH
Traceback (most recent call last):
  File "/Users/dee/ownCloud3/rma2/pyside2_win_main.py", line 12, in <module>
    class MainWindow(QMainWindow, loadUiType("win_main.ui")[0]):
TypeError: 'NoneType' object is not subscriptable

File structure for simplicity of test case:

/Users/dee/ownCloud3/rma2/pyside2_win_main.py
/Users/dee/ownCloud3/rma2/win_main.ui

PySide2 version 15.5.0, shiboken2==5.15.0.

macOS Calatina v10.15.06

Python 3.8.5 64bit (downloaded from here , no HomeBrew etc.

Answer 1

Don't use relative paths as they are susceptible to errors as it will depend on how the script is run, instead build an absolute path:

import os.path


CURRENT_DIR = os.path.dirname(os.path.realpath(__file__))
ui_file_path = os.path.join(CURRENT_DIR, "win_main.ui")


Ui_Class, _ = loadUiType(ui_file_path)


class MainWindow(QMainWindow, Ui_Class):
    # ...

Also add at the top of your file, since it seems that when python was installed, the option to add the necessary paths to the environment variables was not marked:

import PySide2 
import os.path  

uic_dir = os.path.dirname(PySide2.__file__) 
os.environ["PATH"] += os.pathsep + uic_dir