How to control/drive/interact a PyQt GUI from command line in Python

Question

I have a GUI application created with PyQt and I would like to be able to control it also from the python terminal through a kind of internal API.

Ideas :

Answer 1

Depending on what you seem to ask, you want to implement something similar to Native Messaging Protocol_{(Chrome, Mozilla)}, if so, then you should use QWinEventNotifier or QSocketNotifier depending on the OS to detect if it was written on the console.

Based on my previous answer I created the following example where the user writes in the console some phrase and press Enter then that phrase is shown in the QLabel (I have only tested my example in Linux).

import platform
import sys

from PyQt5 import QtCore, QtGui, QtWidgets


class NativeMessenger(QtCore.QObject):
    messageChanged = QtCore.pyqtSignal(str)

    def __init__(self, parent=None):
        super().__init__(parent)

        self.m_qin = QtCore.QFile()

        self.m_qin.open(
            sys.stdin.fileno(), QtCore.QIODevice.ReadOnly | QtCore.QIODevice.Unbuffered
        )

        if platform.system() == "Windows":
            import win32api

            if sys.platform == "win32":
                import os
                import msvcrt

                if platform.python_implementation() == "PyPy":
                    os.fdopen(fh.fileno(), "wb", 0)
                else:
                    msvcrt.setmode(sys.stdin.fileno(), os.O_BINARY)

            self.m_notifier = QtCore.QWinEventNotifier(
                win32api.GetStdHandle(win32api.STD_INPUT_HANDLE)
            )

        else:
            self.m_notifier = QtCore.QSocketNotifier(
                sys.stdin.fileno(), QtCore.QSocketNotifier.Read, self
            )

        self.m_notifier.activated.connect(self.readyRead)

    @QtCore.pyqtSlot()
    def readyRead(self):
        line = self.m_qin.readLine().data().decode().strip()
        self.messageChanged.emit(line)


if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)

    w = QtWidgets.QLabel(alignment=QtCore.Qt.AlignCenter)
    w.resize(640, 480)
    w.show()

    messenger = NativeMessenger()
    messenger.messageChanged.connect(w.setText)

    sys.exit(app.exec_())

Output:

Stack Overflow

The above can be taken as the basis for implementing your API.

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Although another approach is to have 2 applications where a CLI controls the GUI by communicating through sockets and other protocols such as IPC (dbus, etc.), ZeroMQ, MQTT, etc.