PyQt

PyQt is a Python binding of the cross-platform GUI toolkit Qt, implemented as a Python plug-in. PyQt is free software developed by the British firm Riverbank Computing. It is available under similar terms to Qt versions older than 4.5; this means a variety of licenses including GNU General Public License (GPL) and commercial license, but not the GNU Lesser General Public License (LGPL). PyQt supports Microsoft Windows as well as various flavours of UNIX, including Linux and MacOS (or Darwin).

Festures

a substantial set of GUI widgets
classes for accessing SQL databases (ODBC, MySQL, PostgreSQL, Oracle, SQLite)
QScintilla, Scintilla-based rich text editor widget
data aware widgets that are automatically populated from a database
an XML parser
SVG support
classes for embedding ActiveX controls on Windows (only in commercial version)

How to install

$ pip install pyqt5

Hello World example

The below code shows a small window on the screen.

PyQt4

#! /usr/bin/env python3
# Character Encoding: UTF-8
#
# Here we provide the necessary imports.
# The basic GUI widgets are located in QtGui module. 
import sys
from PyQt4.QtGui import QApplication, QWidget

# Every PyQt4 application must create an application object.
# The application object is located in the QtGui module.
app = QApplication(sys.argv)

# The QWidget widget is the base class of all user interface objects in PyQt4.
# We provide the default constructor for QWidget. The default constructor has no parent.
# A widget with no parent is called a window. 
root = QWidget()

root.resize(320, 240)  # The resize() method resizes the widget.
root.setWindowTitle("Hello, World!")  # Here we set the title for our window.
root.show()  # The show() method displays the widget on the screen.

sys.exit(app.exec_())  # Finally, we enter the mainloop of the application.

PyQt5

#! /usr/bin/env python3
# Character Encoding: UTF-8
#
# Here we provide the necessary imports.
# The basic GUI widgets are located in QtWidgets module. 
import sys
from PyQt5.QtWidgets import QApplication, QWidget

# Every PyQt5 application must create an application object.
# The application object is located in the QtWidgets module.
app = QApplication(sys.argv)

# The QWidget widget is the base class of all user interface objects in PyQt5.
# We provide the default constructor for QWidget. The default constructor has no parent.
# A widget with no parent is called a window. 
root = QWidget()

root.resize(320, 240)  # The resize() method resizes the widget.
root.setWindowTitle("Hello, World!")  # Here we set the title for our window.
root.show()  # The show() method displays the widget on the screen.

sys.exit(app.exec_())  # Finally, we enter the mainloop of the application.

Notable applications that use PyQt

Anki, a spaced repetition flashcard program
Calibre, an E-book management application
Dropbox, a file hosting service
Eric Python IDE
fman, cross-platform file manager
Kodos, Python Regular Expression Debugger
Leo, an outliner and literate programming editor
Ninja-IDE, an extensible open-source Python IDE
OpenLP, an open-source lyrics projection program
OpenShot, a video editing program
Orange, a data mining and visualization framework
Puddletag, an open-source, cross-platform ID3 tag editor
QGIS, a free software desktop Geographic Information Systems (GIS) application
qt-recordMyDesktop, Qt4 frontend for recordMyDesktop
Spyder, a Python data science IDE
TortoiseHg, a graphical interface for the Mercurial source management program (Hg)
Veusz, a scientific plotting application

Troubleshooting

Could not find or load the Qt platform plugin

둥기방기의 블로그 :: +) 파이썬 GUI 프로그래밍 with PyQt5 (1)

다음과 같은 에러가 발생할 수 있다.

This application failed to start because it could not find or load the Qt platform plugin "windows".

QT_QPA_PLATFORM_PLUGIN_PATH 환경 변수에 (파이썬3이 설치되어있는 경로)\Lib\site-packages\PyQt5\Qt\plugins\platforms 값을 입력한다.

no Qt platform plugin could be initialized