Question

I am running Emacs 23.2 with python.el and debugging some Python code with pdb.

My code spawns a sibling thread using the threading module and I set a breakpoint at the start of the run() method, but the break is never handled by pdb even though the code definitely runs and works for all intents and purposes.

I was under the impression that I could use pdb to establish breakpoints in any thread, even though full multi-threaded debugging is in fact not supported.

Am I wrong in assuming pdb within an M-x pdb invocation can break within any thread? If you don’t believe me try this minimal example for yourself.

import threading

class ThreadTest(threading.Thread):
    def __init__(self,):
        threading.Thread.__init__(self)

    def run(self):
        print "Type M-x pdb, set a breakpoint here then type c <RET>..."
        print "As you can see it does not break!"

if __name__ == '__main__':
    tt = ThreadTest()

    tt.start()

Thanks to Pierre and the book text he refers to, I tried the option to include pdb.set_trace() as follows:

def run(self):
    import pdb; pdb.set_trace()
    print "Set a breakpoint here then M-x pdb and type c..."

But this only breaks and offers pdb controls for step, next, continue etcetera, if it is executed from a console and run directly within the Python interpreter, and crucially not via M-x pdb – at least with my Emacs and pdb configuration.

So my original question could do with being rephrased:

Is there a way to invoke a Python program from within Emacs, where that program uses inlined invocation of pdb (thereby supporting breaks in multi-threaded applications), and for there to be a pdb comint control buffer established auto-magically?

or

If I run my Python application using M-x pdb and it contains an inline invocation of pdb, how best to handle the fact that this results in a pdb-session-within-a-pdb-session with the associated loss of control?

Answer 1

Are you using the default python.el? I’ve given up on that and started using python-mode.el. Then type M-x shell, from the prompt type python myproblem.py (replace with your program name of course) and it will stop at the set_trace line. It works out of the box with pdb integration. (And it works on your program).