[PyQt] I get a name Name Error: when calling a method inside a class

[Yoriz]

I see a few problems

---

class UiMainWindow(object):
    def __init__(self):
        self.clicked_button = []
        self.main_window = main_window

This is where error you posted is NameError: name 'main_window' is not defined

main_window has not been defined, I think that you mean for main_window to be an attribute passed to the _init__ as shown below

class UiMainWindow(object):
    def __init__(self, main_window):
        self.clicked_button = []
        self.main_window = main_window

once changing that in the following

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    main_window = QtWidgets.QMainWindow()
    ui = UiMainWindow()
    ui.setupUi(main_window)
    main_window.show()
    sys.exit(app.exec_())

ui = UiMainWindow() would need to be passing main_window as ui = UiMainWindow(main_window)

---

In the method

def button_clicked(self):
        button_ = main_window.sender().text()
        self.clicked_button.append(button_)
        return self.clicked_button

button_ = main_window.sender().text() is missing self before main_window

---

Your code outside

input_list = UiMainWindow().button_clicked()
print(input_list)

would need to pass in a main_window
and would not work because

Error:
QWidget: Must construct a QApplication before a QWidget

This would also not be the same instance of the window created in the if __name__ == "__main__":
and at the time you called it there would be no button clicks

An event handler is not meant to return anything, the button click is what calls the method def button_clicked(self): so there is nowhere to return to.

---

I think what you are trying is when a button is clicked use some code outside of the class/instance
you can make a function

def on_button_clicked(input_list):
    print(input_list)

and call it at the end of the button click handler

    def button_clicked(self):
        button_ = self.main_window.sender().text()
        self.clicked_button.append(button_)
        on_button_clicked(self.clicked_button)

---

Here is the full code with the above changes made

# -*- coding: utf-8 -*-
 
# Form implementation generated from reading ui file 'C:\Users\hp\Desktop\PythonLearning\PyQt\Hang\Test_UI_two_buttons.ui'
#
# Created by: PyQt5 UI code generator 5.14.2
#
# WARNING! All changes made in this file will be lost!
 
 
from PyQt5 import QtCore, QtGui, QtWidgets
 
 
class UiMainWindow(object):
    def __init__(self, main_window):
        self.clicked_button = []
        self.main_window = main_window
        self.centralwidget = QtWidgets.QWidget(main_window)
        self.A_Button = QtWidgets.QPushButton(self.centralwidget)
        self.B_Button = QtWidgets.QPushButton(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(main_window)
        self.statusbar = QtWidgets.QStatusBar(main_window)
 
    def setupUi(self, _main__window_):
        _main__window_.setObjectName("MainWindow")
        _main__window_.setEnabled(True)
        _main__window_.resize(863, 600)
        font = QtGui.QFont()
        font.setFamily("MS Sans Serif")
        _main__window_.setFont(font)
        _main__window_.setWindowOpacity(1)
        self.centralwidget.setObjectName("centralwidget")
        self.A_Button.setGeometry(QtCore.QRect(143, 210, 251, 111))
        font = QtGui.QFont()
        font.setFamily("Modern")
        font.setPointSize(10)
        font.setBold(True)
        font.setItalic(True)
        font.setWeight(75)
        self.A_Button.setFont(font)
        self.A_Button.setAutoFillBackground(False)
        self.A_Button.setCheckable(False)
        self.A_Button.setObjectName("A_Button")
        self.B_Button.setGeometry(QtCore.QRect(400, 210, 251, 111))
        font = QtGui.QFont()
        font.setFamily("Modern")
        font.setPointSize(10)
        font.setBold(True)
        font.setItalic(True)
        font.setWeight(75)
        self.B_Button.setFont(font)
        self.B_Button.setObjectName("B_Button")
        _main__window_.setCentralWidget(self.centralwidget)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 863, 21))
        self.menubar.setObjectName("menubar")
        _main__window_.setMenuBar(self.menubar)
        self.statusbar.setObjectName("statusbar")
        _main__window_.setStatusBar(self.statusbar)
 
        self.retranslateUi(_main__window_)
        QtCore.QMetaObject.connectSlotsByName(_main__window_)
 
    def retranslateUi(self, main_window_):
        _translate = QtCore.QCoreApplication.translate
        main_window_.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.A_Button.setText(_translate("MainWindow", "A"))
        self.A_Button.setShortcut(_translate("MainWindow", "A"))
        self.B_Button.setText(_translate("MainWindow", "B"))
        self.B_Button.setShortcut(_translate("MainWindow", "B"))
 
        self.A_Button.clicked.connect(self.button_clicked)
        self.B_Button.clicked.connect(self.button_clicked)
 
    def button_clicked(self):
        button_ = self.main_window.sender().text()
        self.clicked_button.append(button_)
        on_button_clicked(self.clicked_button)
 

def on_button_clicked(input_list):
    print(input_list)
 
 
 
if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    main_window = QtWidgets.QMainWindow()
    ui = UiMainWindow(main_window)
    ui.setupUi(main_window)
    main_window.show()
    sys.exit(app.exec_())

Hopefully, I'm somewhere on track with what you are looking for