Mouse Input
-----------

.. code-block:: python
    :caption: scripts/PYQT4/02_mouse_event/main.py:

    import sys
    from PyQt5.QtWidgets import QApplication, QMainWindow, QLabel
    from PyQt5.QtCore import Qt

    class MouseDetectionApp(QMainWindow):
        def __init__(self):
            super(MouseDetectionApp, self).__init__()

            self.label = QLabel(self)
            self.label.setAlignment(Qt.AlignCenter)
            self.label.setText("Click or move the mouse!")
            self.label.setMouseTracking(True)
            self.setCentralWidget(self.label)

            self.init_ui()

        def init_ui(self):
            self.setWindowTitle('Mouse Event Detection')
            self.setGeometry(100, 100, 400, 300)

        def mousePressEvent(self, event):
            self.label.setText("Mouse Pressed: Button {} at {}".format(event.button(), event.pos()))

        def mouseReleaseEvent(self, event):
            self.label.setText("Mouse Released: Button {} at {}".format(event.button(), event.pos()))

        def mouseMoveEvent(self, event):
            self.label.setText("Mouse Moved: Position {}".format(event.pos()))

        def mouseDoubleClickEvent(self, event):
            self.label.setText("Mouse Double Clicked: Button {} at {}".format(event.button(), event.pos()))

- ``mousePressEvent(event)``: This method is called when a mouse button is pressed. It displays the pressed button and the position of the click.

- ``mouseReleaseEvent(event)``: Called when a mouse button is released. It displays the released button and its position.

- ``mouseMoveEvent(event)``: This is triggered when the mouse moves, displaying its current position.

- ``mouseDoubleClickEvent(event)``: Activated upon a mouse double click. It displays the button double clicked and its position.

- ``self.label.setMouseTracking(True)``: This line ensures that the ``mouseMoveEvent`` is invoked whenever the mouse is moved over the widget. If ``setMouseTracking`` is set to ``False``, the ``mouseMoveEvent`` is only invoked when a mouse button is pressed.

- ``event.button()``: Returns information about the button (left, right, center) related to the mouse event.

- ``event.pos()``: Returns the coordinate information where the mouse event occurred.