How to deactivate all widgets except one on form startup or show?

[Andrew K. Kabaghe]

Dear everyone,
I have designed a QDialog form on which have placed different widgets to do some calculations.
However, everything is working according to plans.
Except that I want to disable all widgets except one for initial input.
I want widgets to follow tab order. After being done entering data, it should trigger or enable the next button to the end.
Previous widgets should loose focus and become disabled as soon as am done with them. But when I click the last button, the first widget should become active again, to allow fresh entry of data.
I used PyQt5 designer version 5.11 to design.