How to update values between PyQt5 Tabs created as classes

Question

I have 2 tabs in PyQT5 created as separate classes. 1 class (tab) is to load excel file, second to set rules for removing unneeded rows. When I load file I need to post all headers to QComboBox in other tab so I can create rules. Can't make that to work.

import sys
from PyQt5.QtWidgets import *
import pandas as pd


class BOMAppWindow(QDialog):
    def __init__(self):
        super().__init__()

        self.setGeometry(250, 150, 1400, 600)

        mainTabWidget = QTabWidget()     # --------- TABS UI ----------
        mainTabWidget.addTab(FileOpenTab(), "File Open")
        mainTabWidget.addTab(RowRemoveRulesTab(), "Row Delete Rules")

        mainVbox = QVBoxLayout()
        mainVbox.addWidget(mainTabWidget)

        self.setLayout(mainVbox)


df = pd.DataFrame()   # pandas dataframe as container for excel spreadsheet
header_list = []


class FileOpenTab(QDialog):
    def __init__(self):
        super().__init__()

        vbox = QVBoxLayout()
        h_top_box = QHBoxLayout()
        excel_load_button = QPushButton("Open Excel File")
        h_top_box.addWidget(excel_load_button)  # ---- Adding Widgets to HBox

        # ----------------  Adding Table Widget -----------

        self.excel_table = QTableWidget()

        vbox.addLayout(h_top_box)         #-----Create Vertical Box Layout
        vbox.addWidget(self.excel_table)
        self.setLayout(vbox)

        excel_load_button.clicked.connect(self.set_file_data)  
# ----------- Open Excel Button Clicked Event
        self.show()

    def file_path(self):       # -----------    file dialog box
        filter_excel_only = "Excel Files (*.xlsx)"
        filename = QFileDialog.getOpenFileName(self, 'Open Excel File', "", filter_excel_only)
        return filename[0]


    def set_file_data(self):                
        path_text = self.file_path()
        if path_text:
            global df
            df = pd.read_excel(path_text, na_filter=False)  
            self.post_dataframe(df)
            RowRemoveRulesTab().update_select_list()

    def post_dataframe(self, dataframe):
        column_count = dataframe.shape[1]
        row_count = dataframe.shape[0]
        self.excel_table.setColumnCount(column_count)
        self.excel_table.setRowCount(row_count)
        self.excel_table.setHorizontalHeaderLabels(list(dataframe.columns))

    def header_list(self):
        return list(df.columns)


class RowRemoveRulesTab(QDialog):
    def __init__(self):
        super().__init__()

        hbox = QHBoxLayout()
        groupBox1 = QGroupBox("Rule 1:")
        vbox1 = QVBoxLayout()

        self.rule1select = QComboBox()
        self.rule1select.addItems(FileOpenTab().header_list())

        vbox1.addWidget(self.rule1select)

        groupBox1.setLayout(vbox1)
        hbox.addWidget(groupBox1)

        self.setLayout(hbox)

        self.show()

    def update_select_list(self):
        self.rule1select.clear()
        self.rule1select.addItems(FileOpenTab().header_list())
        print(FileOpenTab().header_list())


app = QApplication(sys.argv)
bomAppWindow = BOMAppWindow()
bomAppWindow.show()
app.exec()

I need last function in second tab (or any other way to handle it) update_select_list(self): to update QComboBox with header list from excel file loaded in first FileOpenTab class. Now QComboBox remains blank after file load.

Answer 1

The key point of your problem is that you assume that every time you do FileOpenTab() it will always be the same widget but it is not. The same goes for RowRemoveRulesTab. Instead you have to store the object in a variable and reuse it.

On the other hand you have design problems, in this case you must use the Single responsibility principle where it indicates that each class has a function, and must provide methods for other objects to access the information, in Qt/PyQt the simplest way of transmitting information is through signals, in this case when the dataframe is loaded a signal will be emitted with the new headers, and that signal must be connected to a method of the other class so that it updates the information of the QComboBox.

from PyQt5 import QtCore, QtGui, QtWidgets
import pandas as pd


class FileOpenTab(QtWidgets.QWidget):
    headersChanged = QtCore.pyqtSignal(list)

    def __init__(self, parent=None):
        super(FileOpenTab, self).__init__(parent)

        excel_load_button = QtWidgets.QPushButton(
            "Open Excel File", clicked=self.load_file
        )
        self.excel_table = QtWidgets.QTableWidget()

        lay = QtWidgets.QVBoxLayout(self)
        lay.addWidget(excel_load_button)
        lay.addWidget(self.excel_table)

    @QtCore.pyqtSlot()
    def load_file(self):
        filter_excel_only = "Excel Files (*.xlsx)"
        filename, _ = QtWidgets.QFileDialog.getOpenFileName(
            self, "Open Excel File", "", filter_excel_only
        )
        if filename:
            df = pd.read_excel(filename, na_filter=False)
            self.fill_table(df)

    def fill_table(self, dataframe):
        row_count, column_count = dataframe.shape
        self.excel_table.setColumnCount(column_count)
        self.excel_table.setRowCount(row_count)
        headers = list(dataframe.columns)
        self.excel_table.setHorizontalHeaderLabels(headers)
        self.headersChanged.emit(headers)


class RowRemoveRulesTab(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(RowRemoveRulesTab, self).__init__(parent)

        self.rule_select = QtWidgets.QComboBox()
        group_box = QtWidgets.QGroupBox("Rule 1:")

        vbox = QtWidgets.QVBoxLayout()
        vbox.addWidget(self.rule_select)
        group_box.setLayout(vbox)

        lay = QtWidgets.QVBoxLayout(self)
        lay.addWidget(group_box)

    @QtCore.pyqtSlot(list)
    def update_items(self, items):
        self.rule_select.clear()
        self.rule_select.addItems(items)


class BOMAppWindow(QtWidgets.QMainWindow):
    def __init__(self, parent=None):
        super(BOMAppWindow, self).__init__(parent)

        file_open_tab = FileOpenTab()
        row_remove_rules_tab = RowRemoveRulesTab()

        file_open_tab.headersChanged.connect(row_remove_rules_tab.update_items)

        mainTabWidget = QtWidgets.QTabWidget()
        mainTabWidget.addTab(file_open_tab, "File Open")
        mainTabWidget.addTab(row_remove_rules_tab, "Row Delete Rules")

        self.setCentralWidget(mainTabWidget)


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)
    w = BOMAppWindow()
    w.show()
    sys.exit(app.exec_())