PyQt5 - Updating DataFrame behind QTableWidget

Question

I am having problems with the Qt method to update a DataFrame if it has a specific element modified by the user in the GUI.

For example, when I run the following code, I get a 10 by 3 DataFrame with random values displayed. If I try to change any cell to value 400, I double click, type 400 and then press enter. When I print the DataFrame, the value is still the old value. I would like the DataFrame cell to update on user changing the value.

Many thanks!

import sys
import numpy as np
import pandas as pd
from PyQt5.QtWidgets import *
from PyQt5.QtGui import QIcon, QColor
from PyQt5.QtCore import pyqtSlot, Qt, QTimer

class App(QWidget):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        self.setGeometry(700, 100, 350, 380)
        self.createTable()
        self.layout = QVBoxLayout()
        self.layout.addWidget(self.tableWidget)
        self.button = QPushButton('Print DataFrame', self)
        self.layout.addWidget(self.button)
        self.setLayout(self.layout)
        self.button.clicked.connect(self.print_my_df)
        self.tableWidget.doubleClicked.connect(self.on_click_table)
        self.show()

    def createTable(self):
        self.tableWidget = QTableWidget()
        self.df_rows = 10
        self.df_cols = 3
        self.df = pd.DataFrame(np.random.randn(self.df_rows, self.df_cols))
        self.tableWidget.setRowCount(self.df_rows)
        self.tableWidget.setColumnCount(self.df_cols)
        for i in range(self.df_rows):
            for j in range(self.df_cols):
                x = '{:.3f}'.format(self.df.iloc[i, j])
                self.tableWidget.setItem(i, j, QTableWidgetItem(x))

    @pyqtSlot()
    def print_my_df(self):
        print(self.df)

    @pyqtSlot()
    def on_click_table(self):
        for currentQTableWidgetItem in self.tableWidget.selectedItems():
            print((currentQTableWidgetItem.row(), currentQTableWidgetItem.column()))
            self.print_my_df()

if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = App()
    sys.exit(app.exec_())

Answer 1

QTableWidget does not know about the existence of the DataFrame so it is not updating it. We must update it for this we use the cellChanged signal that gives us the row and column, then we use the item() method that returns the QTableWidgetItem given the column and row, then we use the text() method of QTableWidgetItem.

The data that is placed in the items in the user's edition can be of any type for example a text and this would generate an error since the DataFrame only accepts numerical values for this we must provide an input that validates for this we place a QLineEdit with a QDoubleValidator.

class FloatDelegate(QItemDelegate):
    def __init__(self, parent=None):
        QItemDelegate.__init__(self, parent=parent)

    def createEditor(self, parent, option, index):
        editor = QLineEdit(parent)
        editor.setValidator(QDoubleValidator())
        return editor


class TableWidget(QTableWidget):
    def __init__(self, df, parent=None):
        QTableWidget.__init__(self, parent)
        self.df = df
        nRows = len(self.df.index)
        nColumns = len(self.df.columns)
        self.setRowCount(nRows)
        self.setColumnCount(nColumns)
        self.setItemDelegate(FloatDelegate())

        for i in range(self.rowCount()):
            for j in range(self.columnCount()):
                x = '{:.3f}'.format(self.df.iloc[i, j])
                self.setItem(i, j, QTableWidgetItem(x))

        self.cellChanged.connect(self.onCellChanged)

    @pyqtSlot(int, int)
    def onCellChanged(self, row, column):
        text = self.item(row, column).text()
        number = float(text)
        self.df.set_value(row, column, number)

Example:

class App(QWidget):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        self.setGeometry(700, 100, 350, 380)
        df_rows = 10
        df_cols = 3
        df = pd.DataFrame(np.random.randn(df_rows, df_cols))
        self.tableWidget = TableWidget(df, self)

        self.layout = QVBoxLayout()
        self.layout.addWidget(self.tableWidget)
        self.button = QPushButton('Print DataFrame', self)
        self.layout.addWidget(self.button)
        self.setLayout(self.layout)
        self.button.clicked.connect(self.print_my_df)

    @pyqtSlot()
    def print_my_df(self):
        print(self.tableWidget.df)


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = App()
    ex.show()
    sys.exit(app.exec_())