QProcess PyQt5 TypeError

Question

I have an application that uses a lot of QProcess and sometimes two processes run at the same time. That's why I have a lot of functions for readyReadStandardOutput.connect(). so my idea is to create two or three classes for similar situations and reduce code a lot. I have been able to check that in this question, there is a solution that I like

https://stackoverflow.com/questions/41728959....

and there is another one:

https://stackoverflow.com/questions/41728959...

I have tried to create a class that can help me from the class of the first link, however I have not been successful, because it generates error

QObject::connect: Cannot connect ProcessOutputReader::produce_output(QString) to (null)::append_output(QString)
Traceback (most recent call last):
  File "process2.py", line 22, in funRun
    self.process.run_process()
  File "process2.py", line 40, in run_process
    self.process.produce_output.connect(self.append_output)
TypeError: connect() failed between ProcessOutputReader.produce_output[str] and append_output()

this is my code:

import sys
from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *


class windowProcess(QMainWindow):
    def __init__(self):
        super(windowProcess, self).__init__()
        self.setWindowTitle("Windows Process")
        self.resize(475, 253)
        self.btn_run = QPushButton("run",self)
        self.btn_run.setGeometry(388, 20, 75, 25)
        self.text_edit = QTextEdit(self)

        self.text_edit.setGeometry(20, 50, 441, 191)

        self.btn_run.clicked.connect(self.funRun)

    def funRun(self):
        self.process = myClassProcess()
        self.process.run_process()


    @pyqtSlot(str)
    def append_output(self, text):
        self.text_edit.append(text)

    @pyqtSlot(str)
    def append_error(self, text):
        self.text_edit.append(text)


class myClassProcess(object):
    def __init__(self, parent=None):
        self.info = []

    def run_process(self):        
        self.process = ProcessOutputReader()
        cmd = "ping www.google.com"
        self.process.produce_output.connect(self.append_output)
        self.process.produce_error.connect(self.append_error)
        self.process.start(cmd)

    @pyqtSlot(str)
    def append_output(self, text):
        print(text)
        self.info.append(text)
        #return text            

    @pyqtSlot(str)
    def append_error(self, text):
        self.info.append(text)
        #return text            

    def getInfo(self):
        print(self.info)


class ProcessOutputReader(QProcess):
    produce_output = pyqtSignal(str)
    produce_error = pyqtSignal(str)

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

        codec = QTextCodec.codecForLocale()
        self._decoder_stdout = codec.makeDecoder()
        # only necessary when stderr channel isn't merged into stdout:
        self._decoder_stderr = codec.makeDecoder()

        self.readyReadStandardOutput.connect(self._ready_read_standard_output)
        # only necessary when stderr channel isn't merged into stdout:
        self.readyReadStandardError.connect(self._ready_read_standard_error)

    @pyqtSlot()
    def _ready_read_standard_output(self):
        raw_bytes = self.readAllStandardOutput()
        text = self._decoder_stdout.toUnicode(raw_bytes)
        self.produce_output.emit(text)

    # only necessary when stderr channel isn't merged into stdout:
    @pyqtSlot()
    def _ready_read_standard_error(self):
        raw_bytes = self.readAllStandardError()
        text = self._decoder_stderr.toUnicode(raw_bytes)
        self.produce_error.emit(text)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    ventana = windowProcess()
    ventana.show()
    sys.exit(app.exec_())

Answer 1

The pyqtSlot decorator only has meaning for a QObject, in my case myClassProcess is not causing the problem you are pointing out.

Given this there are 2 solutions:

• Do not use @pyqtSlot in append_output and append_error methods of myClassProcess.

• Or make myClassProcess a QObject:

  class myClassProcess(QObject):
      def __init__(self, parent=None):
          super().__init__(parent)
          self.info = []