Hello Julien,
to fix it you have to set the contents margins on the layout object.
so your code should look like this:
....
qh = QtGui.QHBoxLayout( self )
qh.setContentsMargins(0, 0, 0, 0)
self.qlabel = QtGui.QLabel()
self.qlabel.setText( "foobar" )
qh.addWidget( self.qlabel )
....
cheers,
--
paul victor noagbodji