Matigo 0 Light Poster

Hello everyone
I'm building my first app using Python TkInter and i would like to have someone help me with this
I want to make a checkbox by default it should be False (Unchecked)
And make it do something like (Sorry i only know how to do it on visual basic) but just to get the idea

If checkbox1.checked = True then
form.height = 600
form.weight = 400
else
form.height = 500
form.weight = 40

Something like that
thanks in advance