Open up your project files. sometimes emacs can’t find them if you don’t have them open before-hand.
Make sure you have a program called pdb somewhere in your PATH, with the following contents:
#!/bin/sh exec python -m pdb $1 $2 $3 $4 $5 $6 $7 $8 $9
Run M-x pdb in emacs. If you usually run your program as python foo.py , your command line should be pdb foo.py , for twistd and trial just add -b to the command line, e.g.: twistd -b -y my.tac
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: