Message 248194 - Python tracker

Right now breakpoints can only be set/cleared by using a context menu on a line in the editor. I discovered this entirely by reading through the bug database, as right-click doesn't work on OS X (#24801).

Some other tools use an indicator (e.g. stop sign) in the left margin, which can be toggled on and off by a simple click. This could exist in conjunction with line numbering (#17535)