Debugging Python(Twisted) with Emacs

• Open up your project files. sometimes emacs can't find them if you don't have them open before-hand.
• M-x pdb, Run pdb as: twistd -b -f my.tap
• while pdb waits for your input, go to a place in your code and hit C-x SPC to insert a break-point. pdb should say something happy. Do this in as many points as you wish.
• Go to your pdb buffer and hit c; this runs as normal until a break-point is found.
• once you get to a breakpoint, use s to step, n to run the current line without stepping through the functions it calls, w to print out the current stack, u and d to go up and down a level in the stack, p foo to print result of expression foo.
• recommendations for effective debugging:
  • use p self a lot; just knowing the class where the current code is isn't enough most of the time.
  • use w to get your bearings, it'll re-display the current-line/arrow
  • after you use w, use u and d and lots more p self on the different stack-levels.
  • If you've got a big code-path that you need to grok, keep another buffer open and list the code-path there (e.g., I had a nasty-evil Deferred recursion, and this helped me tons)