PyQT5 and Python3 "exit(a.exec_())" NameError: name 'a' is not defined

Question

I am new to python and trying to learn to write a GUI for a raspberry pi. I am currently just following an online tutorial to create a GUI in QT designer. My QT designer has a custom widget that I added from another developer to display an LED in the GUI. The widget/module is qledplugin.py and saved in a "python" folder under the qt5.plugins.designer, and I saved the qled.py under .local.lib.python3.5.site-packages.

I created a basic GUI and the file is saved as mainwindow.ui. I used pyuic to convert it to python3 and saved as mainwindow.py. I then wrote a basic main program called main.py to launch the GUI. There are no functions, it should simply load the GUI I created in a window. The problem I encounter is that when I run python3 main.py I get the following error

myself@my-own-computer:~/Programming/Projects/GenUi$ python3 main.py
    Traceback (most recent call last):
      File "main.py", line 6, in <module>
        import mainwindow
      File "/home/clint/Programming/Projects/GenUi/mainwindow.py", line 86, in <module>
        from qled import QLed
      File "/home/clint/.local/lib/python3.5/site-packages/qled.py", line 398, in <module>
        exit(a.exec_())
    NameError: name 'a' is not defined

The code for qled.py where the error occurs is

if __name__=="__main__":
    from sys import argv, exit
    import sys

    class Test(QWidget):
        def __init__(self, parent=None):
            QWidget.__init__(self, parent)

            self.setWindowTitle("QLed Test")

            _l=QGridLayout()
            self.setLayout(_l)

            self.leds=[]
            for row, shape in enumerate(QLed.shapes.keys()):
                for col, colour in enumerate(QLed.colours.keys()):
                    if colour==QLed.Grey: continue
                    led=QLed(self, onColour=colour, shape=shape)
                    _l.addWidget(led, row, col, Qt.AlignCenter)
                    self.leds.append(led)

            self.toggleLeds()

        def toggleLeds(self):
            for led in self.leds: led.toggleValue()
            QTimer.singleShot(1000, self.toggleLeds)

    a = QApplication(sys.argv)
    t = Test()
    t.show()
    t.raise_()
exit(a.exec_())

at the top of the code for qled.py I have

from PyQt5.QtWidgets import QApplication, QWidget, QGridLayout, QSizePolicy, QStyleOption
from PyQt5.QtCore import pyqtSignal, Qt, QSize, QTimer, QByteArray, QRectF, pyqtProperty
from PyQt5.QtSvg import QSvgRenderer
from PyQt5.QtGui import QPainter

The code for main.py is

import sys
import PyQt5

from PyQt5.QtWidgets import *

import mainwindow

class MainWindow(QMainWindow, mainwindow.Ui_MainWindow):
    def __init__(self):
        super(self.__class__, self).__init__()
    self.setupUi(self)

    def main():
        app = QApplication(sys.argv)
        form = MainWindow()
        form.show()
sys.exit(app.exec_())

if __name__ == "__main__":
    main()

'a' is defined right before the exit, but the program still sees it as undefined. I did have to modify some things for python3 since it was written in python2.7, but I'm new to python and maybe I missed something. All help appreciated.

Answer 1

Python is very strict with indentation. In both cases you have not respected it. In the first case exit (a.exec_()) is on the same level as if __name __ == "__ main__":, this should be inside. In the other case:

def main():
        app = QApplication(sys.argv)
        form = MainWindow()
        form.show()

It is at the same level as the functions of the class, and that is a serious error since it is not a class method; You must move it out.

qled.py

if __name__=="__main__":
    from sys import argv, exit
    import sys

    class Test(QWidget):
        def __init__(self, parent=None):
            QWidget.__init__(self, parent)

            self.setWindowTitle("QLed Test")

            _l=QGridLayout()
            self.setLayout(_l)

            self.leds=[]
            for row, shape in enumerate(QLed.shapes.keys()):
                for col, colour in enumerate(QLed.colours.keys()):
                    if colour==QLed.Grey: continue
                    led=QLed(self, onColour=colour, shape=shape)
                    _l.addWidget(led, row, col, Qt.AlignCenter)
                    self.leds.append(led)

            self.toggleLeds()

        def toggleLeds(self):
            for led in self.leds: led.toggleValue()
            QTimer.singleShot(1000, self.toggleLeds)

    a = QApplication(sys.argv)
    t = Test()
    t.show()
    t.raise_()
    exit(a.exec_())

main.py

import sys
import PyQt5

from PyQt5.QtWidgets import *

import mainwindow

class MainWindow(QMainWindow, mainwindow.Ui_MainWindow):
    def __init__(self):
        super(self.__class__, self).__init__()
    self.setupUi(self)

def main():
    app = QApplication(sys.argv)
    form = MainWindow()
    form.show()
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()