Use variable from other function without "running" the function (Python Qt)

Question

I'm fairly new to Python and I have a question about passing a variable from one function to antother (in a PyQt script).

This is my script:

from PyQt4 import QtCore, QtGui
import analysefuncties
import os

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    def _fromUtf8(s):
        return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, _encoding)
except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName(_fromUtf8("MainWindow"))
        MainWindow.resize(581, 631)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.listWidget_vars = QtGui.QListWidget(self.centralwidget)
        self.listWidget_vars.setGeometry(QtCore.QRect(10, 40, 211, 531))
        #self.listWidget_vars.setAcceptDrops(True)
        self.listWidget_vars.setDragEnabled(True)
        self.listWidget_vars.setDragDropMode(QtGui.QAbstractItemView.DragOnly)
        self.listWidget_vars.setObjectName(_fromUtf8("listWidget_vars"))
        self.label = QtGui.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(20, 10, 101, 20))
        self.label.setObjectName(_fromUtf8("label"))
        self.listWidget_2 = QtGui.QListWidget(self.centralwidget)
        self.listWidget_2.setGeometry(QtCore.QRect(300, 40, 256, 41))
        self.listWidget_2.setAcceptDrops(True)
        self.listWidget_2.setDragDropMode(QtGui.QAbstractItemView.DropOnly)
        self.listWidget_2.setObjectName(_fromUtf8("listWidget_2"))
        self.pushButton = QtGui.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(300, 540, 141, 28))
        self.pushButton.setObjectName(_fromUtf8("pushButton"))
        self.pushButton_2 = QtGui.QPushButton(self.centralwidget)
        self.pushButton_2.setGeometry(QtCore.QRect(470, 540, 90, 28))
        self.pushButton_2.setObjectName(_fromUtf8("pushButton_2"))
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 581, 26))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        self.menuBestand = QtGui.QMenu(self.menubar)
        self.menuBestand.setObjectName(_fromUtf8("menuBestand"))
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(MainWindow)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        MainWindow.setStatusBar(self.statusbar)
        self.actionSelecteer_bestand = QtGui.QAction(MainWindow)
        self.actionSelecteer_bestand.setObjectName(_fromUtf8("actionSelecteer_bestand"))
        self.actionSluit_programma = QtGui.QAction(MainWindow)
        self.actionSluit_programma.setObjectName(_fromUtf8("actionSluit_programma"))
        self.menuBestand.addAction(self.actionSelecteer_bestand)
        self.menuBestand.addAction(self.actionSluit_programma)
        self.menubar.addAction(self.menuBestand.menuAction())

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

        #bind functies aan knoppen
        self.actionSelecteer_bestand.triggered.connect(self.OpenBestand)
        self.pushButton.clicked.connect(self.StartAnalyse)

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow", None))
        self.pushButton.setText(_translate("MainWindow", "Start analyse", None))
        self.pushButton_2.setText(_translate("MainWindow", "Reset", None))
        self.menuBestand.setTitle(_translate("MainWindow", "Bestand", None))
        self.actionSelecteer_bestand.setText(_translate("MainWindow", "Selecteer bestand", None))
        self.actionSluit_programma.setText(_translate("MainWindow", "Sluit programma", None))

    def OpenBestand(self):
        bestand = str(QtGui.QFileDialog.getOpenFileName(None, "Selecteer dataset"))

    def StartAnalyse(self):
        # use 'bestand' from other function, e.g.:
        dataset = bestand
        print dataset

if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    MainWindow = QtGui.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

In "OpenBestand()" I let the user select a file. I want to do something with this file (the path+name) in another function: StartAnalyse. But I cannot do it like the way it is in the script above.

What I can do is returning the variable from OpenBestand() and call it from StartAnalyse():

def OpenBestand(self):
    bestand = str(QtGui.QFileDialog.getOpenFileName(None, "Selecteer dataset"))
    return bestand

def StartAnalyse(self):

    dataset = OpenBestand()
    print dataset

But now everytime I click the button that is connected with 'StartAnalyse' the function 'OpenBestand()' runs and I don't want that. That function belongs to another button.

So I came up with two solutions. Solution 1: make the variable 'bestand' in OpenBestand() global:

def OpenBestand(self):
    global bestand
    bestand = str(QtGui.QFileDialog.getOpenFileName(None, "Selecteer dataset"))


def StartAnalyse(self):
    dataset = bestand
    print dataset # and do stuff with variable (put it in another function)

Solution 2: put path and filename from OpenBestand() in a temporary file and read this file in StartAnalyse() (and os.remove('temfile.txt') it when closing the app):

def OpenBestand(self):
    bestand = str(QtGui.QFileDialog.getOpenFileName(None, "Selecteer dataset"))

    tempf = open('tempfile.txt','w')
    tempf.write(bestand)
    tempf.close()

def StartAnalyse(self):

    tempf = open('tempfile.txt','r')
    dataset = tempf.read()
    tempf.close()

    print dataset

I've read on this forum that declaring global variables is dangerous. So is solution 2 better? Or is there an alternative?

why don't you use self ? self.__bestand = str(QtGui.QFileDialog.getOpenFileName(None, "Selecteer dataset")). Then self.__bestand is visible from the other method. That's what OOP is for. — Jean-François Fabre
– Jean-François Fabre ♦, Commented Mar 24, 2017 at 9:18
Thank you. This works! Can you give me some good documents about OOP? (for beginners...) — Joost
– Joost, Commented Mar 24, 2017 at 9:22
you're already doing OOP when using Qt. You just didn't know it. I cannot really recommend any document. But lookup "python object oriented programming" you'll find stuff — Jean-François Fabre
– Jean-François Fabre ♦, Commented Mar 24, 2017 at 9:28

Jean-François Fabre · Accepted Answer · 2017-03-24 12:18:58Z

1

You should avoid global variables when you can. Here, you can.

Since you're in the same object (identified as self in instance methods), the best way is probably to use a "private" (name-mangled) member to store the value (so it's not easily visible from outside the object), and recall it from the other method.

In __init__(self) add self.__bestand = None so it is defined

Then in your OpenBestand method, assign it:

self.__bestand = str(QtGui.QFileDialog....

and in your StartAnalyse, test to see if it's properly set and use it:

if self.__bestand: # empty or None: won't pass
   # do something
   print(self.__bestand)

edited Mar 24, 2017 at 12:18

answered Mar 24, 2017 at 9:27

Jean-François Fabre♦

141k24 gold badges179 silver badges246 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Joost Over a year ago

Are the two underscores (self.__bestand) necessary? I tried it without them and that works to. Is it a convention or something?

Jean-François Fabre Over a year ago

Kind of. It hides the attribute from the outside of the object.

Harvey Over a year ago

Use one underscore, though. Two is generally considered reserved for Python itself.

Jean-François Fabre Over a year ago

@Harvey no. Using 2 underscores before and after is reserved for Python. 2 underscores before means name-mangled so parent & child class can define the same member without it being shared/overwritten

Collectives™ on Stack Overflow

Use variable from other function without "running" the function (Python Qt)

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related