PySide window does not resize to fit screen

[Hedieh Ebrahimi]

Dear all, 

I am using Pyside to create a user interface for my app. 
The app works fine on my computer with big screen, but when I take it to my laptop with smaller screen size, it does not resize to match the screen size. 

How can I make my main widget get some information about the screen size and resize automatically? 

Thanks in Advance for your answers.