pyqt example pydemo (snippet)

Python pyqt (gui) example 'pydemo'

pydemo

Python pyqt example: pydemo

#!/usr/bin/env python


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##
## Copyright (C) 2013 Riverbank Computing Limited.
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## This file is part of the examples of PyQt.
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from PyQt5.QtCore import pyqtProperty, pyqtSignal, pyqtSlot
from PyQt5.QtWidgets import QApplication, QTextEdit


# The purpose of this class is to show that Designer's property editor shows
# all Python classes in the hierarchy that define properties.
class PyTextViewer(QTextEdit):

    # Initialise the instance.
    def __init__(self, parent=None):
        super(PyTextViewer, self).__init__(parent)

        self.setReadOnly(True)

        # Initialise the author property by calling it's reset function.
        self.resetAuthor()

    # The getter for the author property.  Note that we cannot follow the Qt
    # naming convention (ie. by using the naming the getter "author") because
    # it would conflict with the property name.
    def getAuthor(self):
        return self._author

    # The setter for the author property.
    def setAuthor(self, name):
        self._author = name

    # The resetter for the author property.  Only Qt Designer uses this.  Qt
    # Designer does not use the deleter function of the property.
    def resetAuthor(self):
        self._author = "David Boddie"

    # Define the author property.  This will look like a C++ property to Qt
    # Designer and a Python property to Python.
    author = pyqtProperty(str, getAuthor, setAuthor, resetAuthor)


# This is the class that implements the custom widget.
class PyDemo(PyTextViewer):

    # Define the Qt signals as a sequence of C++ function signatures excluding
    # the return type.  These may be connected to other signals or slots in Qt
    # Designer.
    zoomChanged = pyqtSignal(int)

    # Initialise the instance.
    def __init__(self, parent=None):
        super(PyDemo, self).__init__(parent)

        self.setWindowTitle("PyQt Demonstration Widget")
        self.setText(_demo_text)

        # Initialise the zoom property.  We don't just call the resetter
        # because it assumes that this has already been initialised.
        self._zoom = 0

    # The getter for the zoom property.
    def getZoom(self):
        return self._zoom

    # The setter for the zoom property.  We also make define this as a Qt slot
    # which can be connected to Qt signals in Qt Designer.
    @pyqtSlot(int)
    def setZoom(self, zoom):
        # Don't do anything if nothing has changed.
        if self._zoom == zoom:
            return

        # Zoom in or out according to the relative zoom levels.
        if self._zoom < zoom:
            self.zoomIn(zoom - self._zoom)
        elif self._zoom > zoom:
            self.zoomOut(self._zoom - zoom)

        # Remember the new zoom level.
        self._zoom = zoom

        # Emit the Qt signal to say that the zoom level has changed.
        self.zoomChanged.emit(zoom)

    # The resetter for the zoom property.
    def resetZoom(self):
        self.setZoom(0)

    # Define the zoom property.  Changing the value of this in Qt Designer's
    # property editor causes the zoom level to change dynamically.
    zoom = pyqtProperty(int, getZoom, setZoom, resetZoom)


# The text displayed in the custom widget.
_demo_text = """<h3>PyQt Demonstration Widget</h3>
<p>This simple example demonstrates the following features.</p>
<ul>
 <li>The definition of properties that behave as C++ properties to Qt and
     Python properties to Python.</li>
 <li>The definition of new Qt signals that can be connected to other signals
     and Qt slots in Designer.</li>
 <li>The definition of new Qt slots that can be connected to signals in
     Designer.</li>
</ul>
"""


# Display the custom widget if the script is being run directly from the
# command line.
if __name__ == "__main__":

    import sys

    app = QApplication(sys.argv)

    demo = PyDemo()
    demo.show()

    sys.exit(app.exec_())

Useful links

• Learn PyQt: https://pythonbasics.org/pyqt-hello-world/
• Install PyQt: https://pythonbasics.org/install-pyqt/