PyQt6 Implementing copy-paste functionality across tabs in same window

I have managed to do the following:

1- I treated the main sheet as if it was "just another sheet" and made sure it follows the same relative routine. This included removing unnecessary functions like setUpMainWindow and introducing static values like MAX_ROWS and MAX_COLS for maximum rows and columns respectively. This also entailed renaming extra_sheets_tracker to become sheets_tracker since it will hold all of the sheets.

2- I have created two strategies for pasting: 1st-cell for selecting the first cell in a table, or 1-to-1 for selecting the exact count of cells at the pasting side. This meant, also, checking for the dimensions beforehand and raising the exception Unmatching pasting size if the sizes did not match.

3- I removed self.tab_index and self.copied_cells_list since they are not used. copy_list is used globally and it is not a bad idea to stay in self. However paste_list is not used anywhere else than the paste routine and I removed it from self. You need to look into your self variables, you seem to overuse them.

import sys
from PyQt6.QtWidgets import QApplication, QMainWindow, QTableWidget, QTableWidgetItem, QVBoxLayout, QTabWidget, QWidget, QToolButton, QToolBar
from PyQt6.QtCore import Qt



class MainWindow(QMainWindow):
  def __init__(self):
    super().__init__()
    self.tab_widget = MyTabWidget(self)
    self.setCentralWidget(self.tab_widget)
    self.initializeUI()

  def initializeUI(self):
    """Set up the application's GUI."""
    self.setMinimumSize(1200, 500)
    self.setWindowTitle("Spreadsheet - QTableWidget Example")

    # Used for copy and paste actions
    self.item_text = None
    self.show() 


class MyTabWidget(QWidget):
  def __init__(self, parent):
    super(QWidget, self).__init__(parent)
    self.layout = QVBoxLayout(self)
 
    # Initialize tab screen
    self.MAX_ROWS = 10
    self.MAX_COLS = 10
    self.STRATEGY = {0:'1st-cell', 1:'1-to-1'}
    self.sheets = QTabWidget()
    self.main_sheet = QWidget()
    self.sheets.resize(300, 200)
    self.sheets_tracker = list()
    self.copy_list = []
    #self.copied_cells_list = []
    #self.paste_list = []


    # Add a sheet and create first tab
    self.main_sheet.layout = QVBoxLayout(self)
    # Setup main window
    self.add_sheet()
    
    tabButton = QToolButton(self)
    tabButton.setText('+')
    font = tabButton.font()
    font.setBold(True)
    tabButton.setFont(font)
    tabButton.clicked.connect(self.add_sheet)

    self.sheets.setCornerWidget(tabButton)

    # Add sheets to widget
    self.layout.addWidget(self.sheets)
    self.setLayout(self.layout)

  def add_sheet(self):
    sheets_count = len(self.sheets_tracker)
    if sheets_count < 1:
      label = "Main sheet"
    else:
      label = f"Sheet{sheets_count}"

    self.main_tab_sheet_widget = QTableWidget()
    self.main_tab_sheet_widget.setRowCount(self.MAX_ROWS)
    self.main_tab_sheet_widget.setColumnCount(self.MAX_COLS)
    self.sheets_tracker.append(self.main_tab_sheet_widget)

    self.sheet = QWidget()
    self.sheet.layout = QVBoxLayout(self)
    self.sheet.layout.addWidget(self.main_tab_sheet_widget)
    self.sheet.setLayout(self.sheet.layout)
    self.sheets.addTab(self.main_tab_sheet_widget, label)


  def keyPressEvent(self, event):
    super().keyPressEvent(event)
    if event.key() == Qt.Key.Key_C and (event.modifiers() & Qt.KeyboardModifier.ControlModifier):
      self.copy_list = sorted([(e.row(), e.column(), e.data()) for e in self.sheets_tracker[self.sheets.currentIndex()].selectedIndexes()])
      if len(self.copy_list) != 0:
        # recalculate the indicies to absolute values
        least_row = self.copy_list[0][0]
        least_col = sorted(self.copy_list, key=lambda tup: tup[1])[0][1]
        self.copy_list = [(e[0]-least_row, e[1]-least_col, e[2]) for e in self.copy_list]
        print(self.copy_list)
    elif event.key() == Qt.Key.Key_V and (event.modifiers() & Qt.KeyboardModifier.ControlModifier):
      paste_list = sorted([(element.row(), element.column(), element.data()) for element in self.sheets_tracker[self.sheets.currentIndex()].selectedIndexes()])
      if len(paste_list) != 0:
        if len(paste_list) == 1:
          # The given paste position is the first cell only
          current_r, current_c, _ = paste_list[-1]
          last_r, last_c, _ = self.copy_list[-1]
          if last_r + current_r - 1 < self.MAX_ROWS and last_c + current_c - 1 < self.MAX_COLS:
            strategy = self.STRATEGY[0]
          else:
            raise Exception('Unmatching pasting size')
        elif len(self.copy_list) == len(paste_list):
          # You can paste in one-to-one correspondence
          strategy = self.STRATEGY[1]
        else:
          raise Exception('Unmatching pasting size')
        
        if strategy == self.STRATEGY[0]:
          r, c, _ = paste_list[0]
          for index, e in enumerate(self.copy_list):
            _, _, d = self.copy_list[index]
            d = '' if d is None else d
            print(f"Pasting at index [{self.sheets.currentIndex()}] cell ({e[0]+r}, {e[1]+c})")
            textCell = QTableWidgetItem(); textCell.setText(f'{d}')
            self.sheets_tracker[self.sheets.currentIndex()].setItem(e[0]+r, e[1]+c, textCell)
        
        if strategy == self.STRATEGY[1]:
          for index, e in enumerate(paste_list):
            _, _, d = self.copy_list[index]
            d = '' if d is None else d
            print(f"Pasting at index [{self.sheets.currentIndex()}] cell ({e[0]}, {e[1]})")
            textCell = QTableWidgetItem(); textCell.setText(f'{d}')
            self.sheets_tracker[self.sheets.currentIndex()].setItem(e[0], e[1], textCell)


if __name__ == "__main__":
  app = QApplication(sys.argv)
  window = MainWindow()
  window.show()
  sys.exit(app.exec())