For each button you are doing this:
Then you are expecting the rest of that line
What were you expecting to happen?
self.btn_1 = Button(Form,text="1",width=20,height=7So that sets the text on the button to ( in this case ) 1
Then you are expecting the rest of that line
,command = lambda:self.set_text("1"))to set the text to ( in this case ) 1 which is what it is already set to.
What were you expecting to happen?