>from second ()function I got a number as
>
>35500.572
>
>1-How can I allow only the first four digits
>and prevent from a fractionary number ?
>
>2-Where this number comes from ? As can notice
>it does not match the seconds of my computer panel

I have the feeling that you are mixing the seconds() and sec() functions. Seconds() gives the number of seconds since midnight.

To strip the fractions, you can use int().