Command Window output using Matlab engine in Python

I want to be able to see the output printed in the Command Window in real-time while running a script using the Matlab engine in Python (I'm using the Spyder IDE). I've tried two approaches:

Approach 1:

I've started the Matlab engine with desktop using using the following commands:

eng = matlab.engine.start_matlab()

eng.desktop(nargout=0)

The desktop shows up, however all the output that should show in the Matlab Command Window when I run a Matlab script gets printed in the Spyder IDE console.

Approach 2:

Redirecting the standard output and error from Matlab to Python as described here: https://www.mathworks.com/help/matlab/matlab_external/redirect-standard-output-and-error-to-python.html

When using the approach from this Mathworks example, I have to wait for the Matlab script to finish running to see the output, so it doesn't work in real-time.

Does anyone know how I can make this work using either of these approaches or know of a different way of doing this? I am making a GUI using Pyside that can run some data processing with Matlab, but I want to see the progress printed by the Matlab script as it's running. With approach 2, I would just print the Matlab output to a QTextEdit in Pyside

[Sachin]

Hi

Could you please provide more information about the problem ?

Answer 1

[Emanuel Mendiola]

The example code below generates a simple Python GUI with a QTextEdit and a button that starts the MATLAB engine and runs a MATLAB script that would process data (in this example, it just prints a few things). I want to be able to see the progress of the MATLAB scrip as it's running. For this, I can either start the MATLAB engine in desktop mode and see the MATLAB script output there in the Command Window or print the MATLAB output to the QTextEdit as the script is running.

In the Python script code pasted below, I am running the the script in the background, but when calling future.result() to get the Matlab output/error I have to wait until the Matlab script is finished to get the output/error. So I cannot see the progress of my Matlab script as it's running. Essentially, I want to be able to do this in python:

### pseudocode for desired result

run matlab script

while matlab script is running:

print(matlab script output)

time.sleep(1)

eng.quit()

Alternatively, if I can see the Matlab output in the Command Window, that would also work for me, but when I run the Matlab engine in desktop mode, all the Matlab output is printed on the console window of the Spyder IDE I am using for Python instead.

Python script:

from PySide6.QtWidgets import QApplication,QMainWindow

from PySide6.QtCore import QThread

from PySide6 import QtCore, QtGui, QtWidgets

import io

import matlab.engine

import sys

import time

#GUI is generated

class Ui_MainWindow(object):

def setupUi(self, MainWindow):

MainWindow.setObjectName("MainWindow")

MainWindow.resize(342, 265)

self.centralwidget = QtWidgets.QWidget(MainWindow)

self.centralwidget.setObjectName("centralwidget")

self.gridLayout = QtWidgets.QGridLayout(self.centralwidget)

self.gridLayout.setObjectName("gridLayout")

self.verticalLayout = QtWidgets.QVBoxLayout()

self.verticalLayout.setObjectName("verticalLayout")

self.MatlabConsoleOutTextEdit = QtWidgets.QTextEdit(self.centralwidget)

self.MatlabConsoleOutTextEdit.setObjectName("MatlabConsoleOutTextEdit")

self.verticalLayout.addWidget(self.MatlabConsoleOutTextEdit)

self.StartMatlabButton = QtWidgets.QPushButton(self.centralwidget)

self.StartMatlabButton.setObjectName("StartMatlabButton")

self.verticalLayout.addWidget(self.StartMatlabButton)

self.gridLayout.addLayout(self.verticalLayout, 0, 0, 1, 1)

MainWindow.setCentralWidget(self.centralwidget)

self.menubar = QtWidgets.QMenuBar(MainWindow)

self.menubar.setGeometry(QtCore.QRect(0, 0, 342, 21))

self.menubar.setObjectName("menubar")

MainWindow.setMenuBar(self.menubar)

self.statusbar = QtWidgets.QStatusBar(MainWindow)

self.statusbar.setObjectName("statusbar")

MainWindow.setStatusBar(self.statusbar)

self.retranslateUi(MainWindow)

QtCore.QMetaObject.connectSlotsByName(MainWindow)

def retranslateUi(self, MainWindow):

_translate = QtCore.QCoreApplication.translate

MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))

self.StartMatlabButton.setText(_translate("MainWindow", "StartMatlabButton"))

#Run Matlab processing in separate QThread

class matlabProcThread(QThread):

#create signal to detect finished thread

finished = QtCore.Signal()

#inherit data from GUI to be available for this class

def __init__(self,parent):

super().__init__()

self.parent = parent

def run(self):

#Start Matlab engine

self.eng = matlab.engine.start_matlab()

self.eng.desktop(nargout=0)

#create matlab structure with options for data processing

opt = {}

#data directory

opt['folder'] = 'C:\\Users'

#Nominal bus voltage

opt['Vn'] = 13.2

#Nominal fundamental frequency

opt['F1nom'] = 60.0

#System frequency

opt['F1'] = 59.87

####################################################################################################################################################

###################################################### Matlab Processing and data progress printing ################################################

####################################################################################################################################################

out = io.StringIO()

err = io.StringIO()

#Run the data processing script wrapper that processes options and runs data processing script

future = self.eng.DataProc(opt,stdout=out,stderr=err,nargout=0,background=True)

#Show data processing progress in QTextEdit while the data processing script is running

future.result()

while not future.done():

self.matlabConsoleOutputWrite(out.getvalue())

time.sleep(1)

self.eng.quit()

self.finished.emit()

####################################################################################################################################################

####################################################################################################################################################

####################################################################################################################################################

#function to write text to the console output text field

def matlabConsoleOutputWrite(self, text):

cursor = self.parent.MatlabConsoleOutTextEdit.textCursor()

cursor.movePosition(QtGui.QTextCursor.End)

cursor.insertText(text)

self.parent.MatlabConsoleOutTextEdit.setTextCursor(cursor)

self.parent.MatlabConsoleOutTextEdit.ensureCursorVisible()

#Run GUI process

class MainWindow(QMainWindow, Ui_MainWindow):

def __init__(self,parent=None):

super(MainWindow,self).__init__(parent)

self.setupUi(self) #generate GUI

#Start Matlab data processing when button is clicked

self.StartMatlabButton.clicked.connect(self.startProcessing)

def startProcessing(self):

self.statusBar().showMessage("Processing Data",0)

#Create thread

self.ProcessThread = matlabProcThread(self)

#Enable termination

self.ProcessThread.setTerminationEnabled(True)

#Delete contents after finishing

self.ProcessThread.finished.connect(self.ProcessThread.deleteLater)

#Start thread

self.ProcessThread.start()

#Disable start scan button

self.StartMatlabButton.setEnabled(False)

#Enable start scan button again after thread finishes

self.ProcessThread.finished.connect(lambda: self.StartMatlabButton.setEnabled(True))

self.statusBar().clearMessage()

if __name__ == '__main__':

#initiate app instance

if not QApplication.instance():

app = QApplication(sys.argv)

else:

app = QApplication.instance()

Gui = MainWindow()

Gui.show()

sys.exit(app.exec())

Matlab script:

function DataProc(opt)

disp("starting script")

pause(2)

disp(strcat("option Vn: ",num2str(opt.Vn)))

pause(2)

disp(strcat("option F1nom: ",num2str(opt.F1nom)))

pause(2)

disp(strcat("option F1: ",num2str(opt.F1)))

pause(2)

disp("Starting Data Processing...")

addpath(pwd); % Add current directory to path

cd(opt.folder); % Change directory to folder containing data

%% Postprocessing

%run_processing(opt);

end