Qfyilyi

1. The problem explained

I instantiate a QProcess()-object just before the application shows its main window. The QProcess()-instance is stored in the self.__myProcess variable, and stays alive as long as you can see the main window.

The main window looks like this:

When you click on the button, the following code executes:

def __btn_clicked(self):

    self.__add_openocd_to_env()

    command = "openocd.exe" + 'rn'

    self.__myProcess.start(command)

The last two lines are quite clear: the command openocd.exe is passed to self.__myProcess and executes. What this executable actually does is not important here. In fact, I could use any random executable. The point is: if the executable is in my Windows PATH environment variable, it gets found and executed.

Imagine the executable is NOT in the PATH environment variable. Then the function self.__add_openocd_to_env() should fix that issue:

def __add_openocd_to_env(self):

    env = self.__myProcess.processEnvironment()

    env.insert("PATH", "C:\Users\Kristof\programs\openocd_0.10.0\bin;" + env.value("PATH"))

    self.__myProcess.setProcessEnvironment(env)

However, I've noticed it has no effect at all. I have tried a lot of different things in this function, but it just won't have any effect.

 

You can find the full code here:
_{If you have Python 3 installed with PyQt5, you can simply copy-paste the code into a .py module and run it. You should see the little window with the pushbutton. Of course you should change the path "C:UsersKristof.." to something valid on your computer. You can choose any executable you like for this test.}

import sys

import os

from PyQt5.QtCore import *

from PyQt5.QtGui import *

from PyQt5.QtWidgets import *



class CustomMainWindow(QMainWindow):

    def __init__(self):

        super(CustomMainWindow, self).__init__()

        # -------------------------------- #

        #          QProcess() setup        #

        # -------------------------------- #

        self.__myProcess = QProcess()

        self.__myProcess.setProcessChannelMode(QProcess.MergedChannels)

        self.__myProcess.readyRead.connect(self.__on_output)

        self.__myProcess.errorOccurred.connect(self.__on_error)

        self.__myProcess.finished.connect(self.__on_exit)



        # -------------------------------- #

        #           Window setup           #

        # -------------------------------- #

        self.setGeometry(100, 100, 800, 200)

        self.setWindowTitle("QProcess test")



        self.__frm = QFrame(self)

        self.__frm.setStyleSheet("QWidget { background-color: #ffffff }")

        self.__lyt = QVBoxLayout()

        self.__lyt.setAlignment(Qt.AlignTop)

        self.__frm.setLayout(self.__lyt)

        self.setCentralWidget(self.__frm)



        self.__myBtn = QPushButton("START QPROCESS()")

        self.__myBtn.clicked.connect(self.__btn_clicked)

        self.__myBtn.setFixedHeight(70)

        self.__myBtn.setFixedWidth(200)

        self.__lyt.addWidget(self.__myBtn)

        self.show()



    def __add_openocd_to_env(self):

        env = self.__myProcess.processEnvironment()

        env.insert("PATH", "C:\Users\Kristof\programs\openocd_0.10.0\bin;" + env.value("PATH"))

        self.__myProcess.setProcessEnvironment(env)



    def __btn_clicked(self):

        self.__add_openocd_to_env()

        command = "openocd.exe" + 'rn'

        self.__myProcess.start(command)



    def __on_output(self):

        data = bytes(self.__myProcess.readAll()).decode().replace('rn', 'n')

        print(data)



    def __on_error(self, error):

        print("")

        print("Process error: {0}".format(str(error)))

        print("")





    def __on_exit(self, exitCode, exitStatus):

        print("")

        print("ExitCode = {0}".format(str(exitCode)))

        print("ExitStatus = {0}".format(str(exitStatus)))

        print("")





if __name__ == '__main__':

    app = QApplication(sys.argv)

    QApplication.setStyle(QStyleFactory.create('Fusion'))

    myGUI = CustomMainWindow()

    sys.exit(app.exec_())

2. My question

I know I could simply add "C:UsersKristofprogramsopenocd_0.10.0bin" to my Windows PATH environment variable before instantiating the QProcess(). But that's not the point. I want to know how to add it to the PATH environment variable for that one specific QProcess()-instance. If possible, it should not affect any other QProcess()-instances around in my software, nor should it affect any future QProcess()-instances I create later on.

3. System settings

I use the PyQt5 framework in Python 3.7 on Windows 10.

NOTE:

I've just tried to improve the QProcess() setup in the following way:

        # -------------------------------- #

        #          QProcess() setup        #

        # -------------------------------- #

        self.__myProcess = QProcess()

        self.__myProcess.setProcessChannelMode(QProcess.MergedChannels)

        self.__myProcess.readyRead.connect(self.__on_output)

        self.__myProcess.errorOccurred.connect(self.__on_error)

        self.__myProcess.finished.connect(self.__on_exit)



        # NEW: initialize the environment variables for self.__myProcess:

        env = QProcessEnvironment.systemEnvironment()

        self.__myProcess.setProcessEnvironment(env)

I was hopefull ... but it still won't work :-(
 

 

Based on the comment of Mr. @JonBrave, I have written the following workaround:

import sys

import os

from PyQt5.QtCore import *

from PyQt5.QtGui import *

from PyQt5.QtWidgets import *



class CustomMainWindow(QMainWindow):

    def __init__(self):

        super(CustomMainWindow, self).__init__()

        # -------------------------------- #

        #          QProcess() setup        #

        # -------------------------------- #

        self.__myProcess = QProcess()

        self.__myProcess.setProcessChannelMode(QProcess.MergedChannels)

        self.__myProcess.readyRead.connect(self.__on_output)

        self.__myProcess.errorOccurred.connect(self.__on_error)

        self.__myProcess.finished.connect(self.__on_exit)



        # -------------------------------- #

        #           Window setup           #

        # -------------------------------- #

        self.setGeometry(100, 100, 800, 200)

        self.setWindowTitle("QProcess test")



        self.__frm = QFrame(self)

        self.__frm.setStyleSheet("QWidget { background-color: #ffffff }")

        self.__lyt = QVBoxLayout()

        self.__lyt.setAlignment(Qt.AlignTop)

        self.__frm.setLayout(self.__lyt)

        self.setCentralWidget(self.__frm)



        self.__myBtn = QPushButton("START QPROCESS()")

        self.__myBtn.clicked.connect(self.__btn_clicked)

        self.__myBtn.setFixedHeight(70)

        self.__myBtn.setFixedWidth(200)

        self.__lyt.addWidget(self.__myBtn)

        self.show()



    def __add_openocd_to_env(self):

        self.__oldEnv = os.environ["PATH"]

        os.environ["PATH"] = "C:\Users\Kristof\Dropbox (Personal)\EMBEDOFFICE\embedoffice\resources\programs\openocd_0.10.0_dev00459\bin;" + self.__oldEnv



    def __remove_openocd_from_env(self):

        os.environ["PATH"] = self.__oldEnv



    def __btn_clicked(self):

        self.__add_openocd_to_env()

        command = "openocd.exe" + 'rn'

        self.__myProcess.start(command)

        self.__myProcess.waitForStarted(-1)

        self.__remove_openocd_from_env()



    def __on_output(self):

        data = bytes(self.__myProcess.readAll()).decode().replace('rn', 'n')

        print(data)



    def __on_error(self, error):

        print("")

        print("Process error: {0}".format(str(error)))

        print("")



    def __on_exit(self, exitCode, exitStatus):

        print("")

        print("ExitCode = {0}".format(str(exitCode)))

        print("ExitStatus = {0}".format(str(exitStatus)))

        print("")



if __name__ == '__main__':

    app = QApplication(sys.argv)

    QApplication.setStyle(QStyleFactory.create('Fusion'))

    myGUI = CustomMainWindow()

    sys.exit(app.exec_())

Basically I'm doing the following: just before ordering the QProcess()-instance to start a command, I add the executable path to the PATH environment variable that belongs to the whole Python session. Once the command has started, I can remove it again so it won't have an effect on other QProcess()-instances created in the future.

It works, but it will certainly require a lot of "bookkeeping" if I'm going to apply that approach in my software (many QProcess()-instances live in my software). If you find a better approach, please don't hesitate to share!