How do I structure my PyQt GUI right and call a function while passing the ui?

Question

I'm pretty new to python and especially to pyqt4 but I would like to learn it right.

Therefore I want to build my new learning project in three different files. One main.py file in which I call everything. One by the QDesigner generated UI file (Main_Ui.py) and one Main_Functions.py file in which I would like to keep all my functions.

My first question would therefore be whether this is a "good programming style" or should I do it in a different way?

During the implementation of my idea I got stuck with calling the function. The console says "TypeError: connect() slot argument should be a callable or a signal, not 'NoneType'".

Could you please help me and tell me what I did wrong as I googled now nearly all day long and I could not find anything that would fit or I didn't understood it. It would be really great and would help me a lot learning how to do it right :)

Thank you very much :)

Here is my examplary code so far:

Main.py

import sys
from PyQt4 import QtGui, QtCore
from Main_Ui import Ui_MainWindow
import Main_Functions as f


class MainWindow(QtGui.QMainWindow):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)

        self.ui.btn1.clicked.connect(f.download(self.ui))

if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    myapp = MainWindow()
    myapp.show()
    sys.exit(app.exec_())

Main_Functions.py

def download(window):
    window.completed = 0
    while window.completed < 100:
        window.completed += 0.0001
        window.progress.setValue(window.completed)

And the probably not so interesting Main_Ui.py

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'Main.ui'
#
# Created by: PyQt4 UI code generator 4.11.4
#
# WARNING! All changes made in this file will be lost!

from PyQt4 import QtCore, QtGui

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(1000, 848)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.gridLayoutWidget = QtGui.QWidget(self.centralwidget)
        self.gridLayoutWidget.setGeometry(QtCore.QRect(210, 150, 2, 2))
        self.gridLayoutWidget.setObjectName(_fromUtf8("gridLayoutWidget"))
        self.gridLayout = QtGui.QGridLayout(self.gridLayoutWidget)
        self.gridLayout.setObjectName(_fromUtf8("gridLayout"))
        self.tableWidget = QtGui.QTableWidget(self.centralwidget)
        self.tableWidget.setGeometry(QtCore.QRect(50, 120, 256, 192))
        self.tableWidget.setObjectName(_fromUtf8("tableWidget"))
        self.tableWidget.setColumnCount(1)
        self.tableWidget.setRowCount(1)
        item = QtGui.QTableWidgetItem()
        self.tableWidget.setVerticalHeaderItem(0, item)
        item = QtGui.QTableWidgetItem()
        self.tableWidget.setHorizontalHeaderItem(0, item)
        self.progress = QtGui.QProgressBar(self.centralwidget)
        self.progress.setGeometry(QtCore.QRect(180, 550, 118, 23))
        self.progress.setProperty("value", 24)
        self.progress.setObjectName(_fromUtf8("progress"))
        self.btn1 = QtGui.QPushButton(self.centralwidget)
        self.btn1.setGeometry(QtCore.QRect(490, 200, 75, 23))
        self.btn1.setObjectName(_fromUtf8("btn1"))
        self.lbl1 = QtGui.QLabel(self.centralwidget)
        self.lbl1.setGeometry(QtCore.QRect(400, 200, 46, 13))
        self.lbl1.setObjectName(_fromUtf8("lbl1"))
        self.txt1 = QtGui.QLineEdit(self.centralwidget)
        self.txt1.setGeometry(QtCore.QRect(330, 160, 113, 20))
        self.txt1.setObjectName(_fromUtf8("txt1"))
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 1000, 21))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        self.menuDatei = QtGui.QMenu(self.menubar)
        self.menuDatei.setObjectName(_fromUtf8("menuDatei"))
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(MainWindow)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        MainWindow.setStatusBar(self.statusbar)
        self.actionSchlie_en = QtGui.QAction(MainWindow)
        self.actionSchlie_en.setObjectName(_fromUtf8("actionSchlie_en"))
        self.menuDatei.addAction(self.actionSchlie_en)
        self.menubar.addAction(self.menuDatei.menuAction())

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

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow", None))
        item = self.tableWidget.verticalHeaderItem(0)
        item.setText(_translate("MainWindow", "T", None))
        item = self.tableWidget.horizontalHeaderItem(0)
        item.setText(_translate("MainWindow", "1", None))
        self.btn1.setText(_translate("MainWindow", "PushButton", None))
        self.lbl1.setText(_translate("MainWindow", "TextLabel", None))
        self.menuDatei.setTitle(_translate("MainWindow", "Datei", None))
        self.actionSchlie_en.setText(_translate("MainWindow", "Schließen", None))


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_())

Answer 1

The problem is your connection

self.ui.btn1.clicked.connect(f.download(self.ui))

You need to pass a callback to the connect function. Here, you're actually calling the download function (which returns None) and passing the results to connect.

You need to do this instead

self.ui.btn1.clicked.connect(lambda: f.download(self.ui))

It does often make sense to separate non-gui business logic out into separate modules. This allows them to be re-used in other modules and GUI's. However, in your case, you're performing GUI modification in code outside your GUI class. That's generally not a very good design and it would be better for you to define those functions inside your MainWindow class.