code: def addBreakpoint( self, lineno = -1 ):
          
          if ( lineno == -1 ):
              lineno, colno = self.getCursorPosition()
              
          self.markerAdd(lineno, self._breakpointMarker)
          
          if ( not self.signalsBlocked() ):
              self.breakpointsChanged.emit()
docs: Adds a breakpoint for the given line number to this edit.
          
          :note       The lineno is 0-based, while the editor displays lines as
                      a 1-based system.  So, if you want to put a breakpoint at
                      visual line 3, you would pass in lineno as 2
          
          :param      lineno | <int>