Emacs: methods for debugging python

Posted by Tom Willis on Programmers See other posts from Programmers or by Tom Willis
Published on 2010-12-24T18:16:10Z Indexed on 2010/12/31 2:00 UTC
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I use emacs for all my code edit needs. Typically, I will use M-x compile to run my test runner which I would say gets me about 70% of what I need to do to keep the code on track however lately I've been wondering how it might be possible to use M-x pdb on occasions where it would be nice to hit a breakpoint and inspect things.

In my googling I've found some things that suggest that this is useful/possible. However I have not managed to get it working in a way that I fully understand.

I don't know if it's the combination of buildout + appengine that might be making it more difficult but when I try to do something like

M-x pdb
Run pdb (like this): /Users/twillis/projects/hydrant/bin/python /Users/twillis/bin/pdb /Users/twillis/projects/hydrant/bin/devappserver /Users/twillis/projects/hydrant/parts/hydrant-app/

Where .../bin/python is the interpreter buildout makes with the path set for all the eggs.

~/bin/pdb is a simple script to call into pdb.main using the current python interpreter

HellooKitty:hydrant twillis$ cat ~/bin/pdb
#! /usr/bin/env python

if __name__ == "__main__":
    import sys
    sys.version_info
    import pdb
    pdb.main()
HellooKitty:hydrant twillis$ 

.../bin/devappserver is the dev_appserver script that the buildout recipe makes for gae project and .../parts/hydrant-app is the path to the app.yaml

I am first presented with a prompt

Current directory is /Users/twillis/bin/
C-c C-f

Nothing happens but

HellooKitty:hydrant twillis$ ps aux | grep pdb
twillis    469 100.0  1.6   168488  67188 s002  Rs+   1:03PM   0:52.19 /usr/local/bin/python2.5 /Users/twillis/projects/hydrant/bin/python /Users/twillis/bin/pdb /Users/twillis/projects/hydrant/bin/devappserver /Users/twillis/projects/hydrant/parts/hydrant-app/
twillis    477   0.0  0.0  2435120    420 s000  R+    1:05PM   0:00.00 grep pdb
HellooKitty:hydrant twillis$ 

something is happening

C-x [space]

will report that a breakpoint has been set. But I can't manage to get get things going.

It feels like I am missing something obvious here. Am I?

So, is interactive debugging in emacs worthwhile? is interactive debugging a google appengine app possible? Any suggestions on how I might get this working?

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