Chapter 4 - Add a QTableView

Now that you have a QMainWindow, you can include a centralWidget to your interface. Usually, a QWidget is used to display data in most data-driven applications. Use a table view to display your data.

The first step is to add a horizontal layout with just a QTableView. You can create a QTableView object and place it inside a QHBoxLayout. Once the QWidget is properly built, pass the object to the QMainWindow as its central widget.

Remember that a QTableView needs a model to display information. In this case, you can use a QAbstractTableModel instance.

Note

You could also use the default item model that comes with a QTableWidget instead. QTableWidget is a convenience class that reduces your codebase considerably as you don’t need to implement a data model. However, it’s less flexible than a QTableView, as QTableWidget cannot be used with just any data. For more insight about Qt’s model-view framework, refer to the Model View Programming <http://doc.qt.io/qt-5/model-view-programming.html> documentation.

Implementing the model for your QTableView, allows you to: - set the headers, - manipulate the formats of the cell values (remember we have UTC time and float numbers), - set style properties like text alignment, - and even set color properties for the cell or its content.

To subclass the QAbstractTable, you must reimplement its virtual methods, rowCount(), columnCount(), and data(). This way, you can ensure that the data is handled properly. In addition, reimplement the headerData() method to provide the header information to the view.

Here is a script that implements the CustomTableModel:

from PySide2.QtCore import Qt, QAbstractTableModel, QModelIndex
from PySide2.QtGui import QColor


class CustomTableModel(QAbstractTableModel):
    def __init__(self, data=None):
        QAbstractTableModel.__init__(self)
        self.load_data(data)

    def load_data(self, data):
        self.input_dates = data[0].values
        self.input_magnitudes = data[1].values

        self.column_count = 2
        self.row_count = len(self.input_magnitudes)

    def rowCount(self, parent=QModelIndex()):
        return self.row_count

    def columnCount(self, parent=QModelIndex()):
        return self.column_count

    def headerData(self, section, orientation, role):
        if role != Qt.DisplayRole:
            return None
        if orientation == Qt.Horizontal:
            return ("Date", "Magnitude")[section]
        else:
            return "{}".format(section)

    def data(self, index, role=Qt.DisplayRole):
        column = index.column()
        row = index.row()

        if role == Qt.DisplayRole:
            if column == 0:
                raw_date = self.input_dates[row]
                date = "{}".format(raw_date.toPython())
                return date[:-3]
            elif column == 1:
                return "{:.2f}".format(self.input_magnitudes[row])
        elif role == Qt.BackgroundRole:
            return QColor(Qt.white)
        elif role == Qt.TextAlignmentRole:
            return Qt.AlignRight

        return None

Now, create a QWidget that has a QTableView, and connect it to your CustomTableModel.

from PySide2.QtWidgets import (QHBoxLayout, QHeaderView, QSizePolicy,
                               QTableView, QWidget)

from table_model import CustomTableModel


class Widget(QWidget):
    def __init__(self, data):
        QWidget.__init__(self)

        # Getting the Model
        self.model = CustomTableModel(data)

        # Creating a QTableView
        self.table_view = QTableView()
        self.table_view.setModel(self.model)

        # QTableView Headers
        self.horizontal_header = self.table_view.horizontalHeader()
        self.vertical_header = self.table_view.verticalHeader()
        self.horizontal_header.setSectionResizeMode(
                               QHeaderView.ResizeToContents
                               )
        self.vertical_header.setSectionResizeMode(
                             QHeaderView.ResizeToContents
                             )
        self.horizontal_header.setStretchLastSection(True)

        # QWidget Layout
        self.main_layout = QHBoxLayout()
        size = QSizePolicy(QSizePolicy.Preferred, QSizePolicy.Preferred)

        ## Left layout
        size.setHorizontalStretch(1)
        self.table_view.setSizePolicy(size)
        self.main_layout.addWidget(self.table_view)

        # Set the layout to the QWidget
        self.setLayout(self.main_layout)

You also need minor changes to the main_window.py and main.py from chapter 3 to include the Widget inside the MainWindow.

In the following snippets you’ll see those changes highlighted:

from PySide2.QtCore import Slot
from PySide2.QtGui import QKeySequence
from PySide2.QtWidgets import QMainWindow, QAction


class MainWindow(QMainWindow):
    def __init__(self, widget):
        QMainWindow.__init__(self)
        self.setWindowTitle("Eartquakes information")
        self.setCentralWidget(widget)
        # Menu
        self.menu = self.menuBar()
        self.file_menu = self.menu.addMenu("File")

        ## Exit QAction
        exit_action = QAction("Exit", self)
        exit_action.setShortcut(QKeySequence.Quit)
        exit_action.triggered.connect(self.close)

        self.file_menu.addAction(exit_action)

        # Status Bar
        self.status = self.statusBar()
        self.status.showMessage("Data loaded and plotted")

        # Window dimensions
        geometry = qApp.desktop().availableGeometry(self)
        self.setFixedSize(geometry.width() * 0.8, geometry.height() * 0.7)

import sys
import argparse
import pandas as pd

from PySide2.QtCore import QDateTime, QTimeZone
from PySide2.QtWidgets import QApplication
from main_window import MainWindow
from main_widget import Widget


def transform_date(utc, timezone=None):
    utc_fmt = "yyyy-MM-ddTHH:mm:ss.zzzZ"
    new_date = QDateTime().fromString(utc, utc_fmt)
    if timezone:
        new_date.setTimeZone(timezone)
    return new_date


def read_data(fname):
    # Read the CSV content
    df = pd.read_csv(fname)

    # Remove wrong magnitudes
    df = df.drop(df[df.mag < 0].index)
    magnitudes = df["mag"]

    # My local timezone
    timezone = QTimeZone(b"Europe/Berlin")

    # Get timestamp transformed to our timezone
    times = df["time"].apply(lambda x: transform_date(x, timezone))

    return times, magnitudes


if __name__ == "__main__":
    options = argparse.ArgumentParser()
    options.add_argument("-f", "--file", type=str, required=True)
    args = options.parse_args()
    data = read_data(args.file)

    # Qt Application
    app = QApplication(sys.argv)

    widget = Widget(data)
    window = MainWindow(widget)
    window.show()

    sys.exit(app.exec_())