用PyQt5做图形界面（一）Hello world

# 建立python虚拟环境
python3 -m venv venv
# 激活虚拟环境
source ./venv/bin/activate
# 通过阿里云pypi镜像安装PyQt5库
pip3 install -i https://mirrors.aliyun.com/pypi/simple PyQt5
# 查看安装了哪些第三方库
pip3 list

import sys
from PyQt5.QtWidgets import (QApplication,
                             QWidget,
                             QVBoxLayout,
                             QLineEdit,
                             QPushButton)

# create an app
app = QApplication(sys.argv)

# create an empty window
window = QWidget()

# create a vertical box to contain all gui components, and add vbox to window
vbox = QVBoxLayout()
window.setLayout(vbox)

# create a line edit in vbox
edit = QLineEdit()
vbox.addWidget(edit)

# define a handle function for button
def say_hello():
    txt = edit.text()
    print('Hello ' + txt)

# create a button, and connect clicked event to the handle function in vbox
button = QPushButton("Click Me")
button.clicked.connect(say_hello)
vbox.addWidget(button)

# show window and execute app
window.show()
ret = app.exec_()

# exit after the window is closed
sys.exit(ret)