How to set widget size as a percentage in PyQt5?

Question

Python

I want the widget to be 20% long and 100% high

Answer 1

As a percentage of what?
For widgets in the layout set strech parameters

widg1.setHorizontalStretch(1)
widg2.setHorizontalStretch(2)

Inside the layout, the sizes of the widgets widg1 and widg2 will be determined by the ratio of the numbers specified in setHorizontalStretch, in this case, the horizontal sizes will be 1 to 2. widg 1 will be 2 times smaller than the second widget
It is desirable to set SizePolicy as Preferred

Answer 2

In addition, you can play around with QSS styles.
As an example

checkbutton.setStyleSheet("QPushButton {background-color:rgb(0,200,0) ; color: White; border-radius: 3px; height:15%; width:70%} "
                                  "QPushButton:pressed {background-color:rgb(0,150,0) ; }")

But the primary layout by region is above all.