Qt for Python

Integrated Computer Solutions Inc. www.ics.com
Qt for Python
March 21, 2019
Copyright 2019, Integrated Computers Solutions, Inc.
This work may not be reproduced in whole or in part without the express written consent of Integrated Computer Solutions, Inc.
1

What is Qt for Python?
• Also known as PySide 2
• Qt for Python are the Python v2 and v3 bindings for Qt
• Qt for Python gives the Python programmer access to the full Qt API
• API is the same from C++
• Qt for Python is available under the LGPL v3 and the Qt Commercial License.
• Owned and distributed by The Qt Company
2

Other Features
• The APIs are almost identical to C++, so experienced Qt users can quickly get
up to speed and leverage their Qt knowledge.
• You can continue to use Qt Designer .ui files and resources.
• If you are porting a C++ application, you can mostly one for one port much of
the code.
• Run time errors are usually straightforward.
• A developer can be very productive due to not needing a compile/build cycle.
https://www.ics.com/blog/we-ported-qt-app-c-python-heres-what-happened
3

Confusion with PyQt
• PyQt is another product that provides Python bindings to Qt (and is mostly
compatible with PySide)
• PyQt is dual licensed on all supported platforms under the GNU GPL v3 and
the Riverbank Commercial License (LGPL not available)
• PyQt is owned and distributed by Riverbank
• Differences between Python for Qt and PyQt are discussed here:
https://machinekoder.com/pyqt-vs-qt-for-python-pyside2-pyside/
4

What is Qt?
• Cross-Platform C++ class library
• Encompasses some 1,500 C++ classes
• Started as a Graphics User Interface (GUI) toolkit
• Is much more today: Threads, XML/JSON parsing, Regular Expressions, Sockets, HTML parsing
• Development for Desktop and Embedded Devices
• Qt is available under commercial and open source licenses
• In addition to class libraries, Qt framework contains several tools, like Qt Creator (IDE), Qt Designer,
qmake, Qt Linguist
• Owned and distributed by The Qt Company
5

How to Install
• After you have installed Python,
• Python install is in your path
• Other ways to install (including building):
https://wiki.qt.io/Qt_for_Python/GettingStarted
pip install PySide2
6

“Hello World” in Pyside 2 — Widget-Based
#!/usr/bin/env python3
import sys
from PySide2.QtWidgets import QApplication, QPushButton
if __name__ == '__main__':
app = QApplication(sys.argv)
button = QPushButton(None) #Creates a widget
button.setText("Hello world")
button.show()
sys.exit(app.exec_()) #Starts the event loop
Program consists of:
• py_qtsimple.py
7

A First Example with Widgets
class customWidget(QtWidgets.QWidget):
def __init__(self):
QtWidgets.QWidget.__init__(self)
self.setWindowTitle(self.tr("My First Example"))
self.label = QtWidgets.QLabel("Note:", self)
self.edit = QtWidgets.QTextEdit(self)
self.clear = QtWidgets.QPushButton("Clear", self)
self.save = QtWidgets.QPushButton("Save", self)
# Widget layout
self.outer = QtWidgets.QVBoxLayout()
self.outer.addWidget(self.label)
self.outer.addWidget(self.edit)
self.inner = QtWidgets.QHBoxLayout()
self.inner.addWidget(self.clear)
self.inner.addWidget(self.save)
self.setLayout(self.outer)
# Nesting layouts
self.outer.addLayout(self.inner)
8

“Hello World” in Pyside2 — Qt Quick-Based
9
#!/usr/bin/env python3
import sys
from PySide2.QtCore import QUrl
from PySide2.QtQuick import QQuickView
from PySide2.QtWidgets import QApplication
if __name__ == '__main__':
app = QApplication(sys.argv)
view = QQuickView()
view.setSource(QUrl('main.qml'))
view.show() # window created in QML
sys.exit(app.exec_())
Program consists of
• HelloWorldQML.py – creation and startup of the QML engine (with executable
permissions)
• main.qml – application code

Qt Creator IDE
● Advanced C++, QML and Python code
editor
● 100% open source, written in Qt 5
● Integrated GUI layout and form designer
● Rapid code
navigation tools
● Supports multiple
Platforms
● Downloadable here
https://www.qt.io/offline-installers
10

Qt Components
List of available Qt modules are here:
https://doc.qt.io/qtforpython/?hsCtaTracking=fab9e910-0b90-4caa-b6d0-e202692b6f13%7Cb9e0be8d-1
d85-4644-aaa2-41de4e6d37e3#qt-modules
11

Use of Qt Designer
12
import sys
from PySide2 import QtWidgets
from form import Ui_Form
class MyForm(QtWidgets.QWidget):
def __init__(self, parent=None):
QtWidgets.QWidget.__init__(self, parent)
self.ui = Ui_Form()
self.ui.setupUi(self)
if __name__ == "__main__":
app = QtWidgets.QApplication(sys.argv)
myapp = MyForm()
myapp.ui.pushButton.clicked.connect(app.quit)
myapp.show()
• Requires the compilation of a form:
pyside2-uic.exe form.ui > form.py

Use of Qt Designer with UILoader
from PySide2.QtUiTools import QUiLoader
from PySide2 import QtWidgets
from PySide2.QtCore import QFile
class MyForm(QtWidgets.QWidget):
QtWidgets.QWidget.__init__(self, parent)
file = QFile("form.ui")
file.open(QFile.ReadOnly)
self.loader = QUiLoader()
self.myWidget = self.loader.load(file, self)
file.close()
layout = QtWidgets.QVBoxLayout()
layout.addWidget(self.myWidget)
self.setLayout(layout)
if __name__ == "__main__":
app = QtWidgets.QApplication(sys.argv)
myapp = MyForm()
myapp.show()
13

Signals and Slots
from PySide2.QtCore import SIGNAL, QObject
# define a new slot that receives a string and has
# 'saySomeWords' as its name
@Slot(str)
def say_some_words(words):
print(words)
class Communicate(QObject):
# create a new signal on the fly and name it 'speak'
speak = Signal(str)
someone = Communicate()
# connect signal and slot
someone.speak.connect(say_some_words)
# emit 'speak' signal
someone.speak.emit("Hello everybody!")
See https://wiki.qt.io/Qt_for_Python_Signals_and_Slots
14

Reimplementing Events
from PySide2.QtWidgets import QWidget
from PySide2.QtCore import Qt, Signal
class MainWidget(QWidget):
QWidget.__init__(self, parent)
self.resize(400, 300)
self.setWindowTitle("Widget Event Example")
self.setFocusPolicy(Qt.StrongFocus)
def mousePressEvent(self, event):
if self.m_logAll:
self.notifyEvent['QString', 'QEvent'].emit("mousePressEvent", event)
super(MainWidget, self).mousePressEvent(event)
15

The Property System
from PySide2.QtCore import QObject, Signal, Property
class Person(QObject):
def __init__(self, name):
QObject.__init__(self)
self._person_name = name
def _name(self):
return self._person_name
@Signal
def name_changed(self):
pass
name = Property(str, _name, notify=name_changed)
• Useful in QML
16

Some Notes to Keep in Mind
• No QString, use Python string (str)
• The Qt container classes are not available, use the ones provided by Python
• Some Qt method names Qt names have had an underscore appended to
resolve this conflict (i.e. QTextStream methods bin_(), hex_(), oct_() and
QDialog exec_())
• No QVariants! Any Qt function expecting or returning a QVariant can receive
or return any Python object
17

Business Logic/UI Paradigm
18
Business Logic
Python
UI in Python
(Widgets)
Or QML

When to Use Non-GUI PySide 2
• Dealing with not blocking your GUI (QProcess, networking, QSerial vs.
PySerial, etc.)
• QSqlDatabase because you want to show it in a QTableView
• Better integration with Qt in general (e.g. QThread)
19

Where to Get Help
• https://qmlbook.github.io/ch18-python/python.html
• PySide2 Mailing List https://lists.qt-project.org/mailman/listinfo/pyside
• AppDataLocalProgramsPythonPython37-32Libsite-packagesPySide2
examples
• Tutorial: https://build-system.fman.io/python-qt-tutorial
20

Programming with Qt for Python Training Course
● New 5-day hands-on introduction to developing desktop applications using
the official set of Python bindings covering:
● GUI programming
● GraphicsView
● Model/View
● Challenges inherent to mixing the Qt API with Python
● May 13 - 17 - Waltham, MA
● June 24 - 28, Sunnyvale, CA
● https://www.ics.com/learning/training/programming-qt-python
21

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