**Course Title:** PySide6 Application Development **Section Title:** Handling Files and User Input **Topic:** Building an app that allows file selection and file content reading and writing.(Lab topic) **Introduction** In this lab, we'll build a PySide6 application that allows users to select files, read their contents, and write new data to the files. This will involve working with `QFileDialog` for file selection, `QFile` and `QTextStream` for file I/O operations, and PySide6's event-driven programming model to handle user interactions. **File Selection with QFileDialog** Before reading and writing file contents, we need to let the user select the files they're interested in. `QFileDialog` provides an easy-to-use interface for file selection. We'll create a `QPushButton` that opens a file dialog when clicked. ```python import sys from PySide6.QtWidgets import QApplication, QWidget, QPushButton, QVBoxLayout, QFileDialog class FileSelector(QWidget): def __init__(self): super().__init__() self.initUI() def initUI(self): layout = QVBoxLayout() self.setLayout(layout) select_button = QPushButton("Select File") select_button.clicked.connect(self.select_file) layout.addWidget(select_button) self.show() def select_file(self): file_name, _ = QFileDialog.getOpenFileName(self, "Select File", "", "All Files (*)") if file_name: print("Selected File:", file_name) if __name__ == "__main__": app = QApplication(sys.argv) file_selector = FileSelector() sys.exit(app.exec()) ``` **Reading File Contents with QFile and QTextStream** Once we have the selected file's path, we can read its contents using `QFile` and `QTextStream`. We'll modify the `FileSelector` class to read the selected file's contents and display them in a `QTextEdit` widget. ```python import sys from PySide6.QtWidgets import QApplication, QWidget, QPushButton, QVBoxLayout, QFileDialog, QTextEdit class FileSelector(QWidget): def __init__(self): super().__init__() self.initUI() def initUI(self): layout = QVBoxLayout() self.setLayout(layout) select_button = QPushButton("Select File") select_button.clicked.connect(self.select_file) layout.addWidget(select_button) self.text_edit = QTextEdit() layout.addWidget(self.text_edit) self.show() def select_file(self): file_name, _ = QFileDialog.getOpenFileName(self, "Select File", "", "All Files (*)") if file_name: self.read_file_contents(file_name) def read_file_contents(self, file_name): try: with open(file_name, "r") as file: file_contents = file.read() self.text_edit.setText(file_contents) except Exception as e: print("Error reading file:", e) if __name__ == "__main__": app = QApplication(sys.argv) file_selector = FileSelector() sys.exit(app.exec()) ``` **Writing New Data to Files with QFile and QTextStream** To write new data to files, we'll add a `QPushButton` that saves the current text in the `QTextEdit` widget to the selected file. We'll use `QFile` and `QTextStream` to write the text to the file. ```python import sys from PySide6.QtWidgets import QApplication, QWidget, QPushButton, QVBoxLayout, QFileDialog, QTextEdit class FileSelector(QWidget): def __init__(self): super().__init__() self.initUI() def initUI(self): layout = QVBoxLayout() self.setLayout(layout) select_button = QPushButton("Select File") select_button.clicked.connect(self.select_file) layout.addWidget(select_button) self.text_edit = QTextEdit() layout.addWidget(self.text_edit) save_button = QPushButton("Save Changes") save_button.clicked.connect(self.save_changes) layout.addWidget(save_button) self.show() def select_file(self): file_name, _ = QFileDialog.getOpenFileName(self, "Select File", "", "All Files (*)") if file_name: self.read_file_contents(file_name) self.file_name = file_name def read_file_contents(self, file_name): try: with open(file_name, "r") as file: file_contents = file.read() self.text_edit.setText(file_contents) except Exception as e: print("Error reading file:", e) def save_changes(self): if hasattr(self, "file_name"): try: with open(self.file_name, "w") as file: file.write(self.text_edit.toPlainText()) print("Changes saved") except Exception as e: print("Error writing to file:", e) if __name__ == "__main__": app = QApplication(sys.argv) file_selector = FileSelector() sys.exit(app.exec()) ``` **Conclusion** In this lab, we've built a PySide6 application that allows users to select files, read their contents, and write new data to the files using `QFileDialog`, `QFile`, and `QTextStream`. This demonstrates how to handle file I/O operations in PySide6 and provides a solid foundation for building more complex applications. For more information on PySide6 and its features, please visit the official [PySide6 documentation](https://doc.qt.io/qtforpython-6/).