PyQt5

• QWidget is the base class for all user interface objects or widgets.

• QGridLayout 中的参数，前两个：row,col
  后两个：rowSpan,columnSpan

• FormLayout

  layout.addRow('Name:', QLineEdit())

• If your slot function needs to receive extra arguments, then you can pass them in by using functools.partial. For example, you can modify greeting() as follows:

def greeting(who):
    """Slot function."""
    if msg.text():
        msg.setText('')
    else:
        msg.setText(f'Hello {who}')

btn.clicked.connect(functools.partial(greeting, 'World!'))

• You can’t create a main window without first setting a central widget. You must have a central widget, even if it’s just a placeholder.