- Image via Wikipedia
My goal is to get the pdb shell from the worker processes i spawned with Process() from python-processing. The “classic” approach to spawning the pdb shell miserably fails:
(Pdb) > /home/redduck666/dev/abj/bin/feeds.py(639)__init__() -> self.timeout = timeout Process Process-3:2: Traceback (most recent call last): File "/var/lib/python-support/python2.5/processing/process.py", line 227, in _bootstrap self.run() File "/var/lib/python-support/python2.5/processing/process.py", line 85, in run self._target(*self._args, **self._kwargs) File "./feeds.py", line 639, in __init__ self.timeout = timeout File "./feeds.py", line 639, in __init__ self.timeout = timeout File "/usr/lib/python2.5/bdb.py", line 48, in trace_dispatch return self.dispatch_line(frame) File "/usr/lib/python2.5/bdb.py", line 66, in dispatch_line self.user_line(frame) File "/usr/lib/python2.5/pdb.py", line 144, in user_line self.interaction(frame, None) File "/usr/lib/python2.5/pdb.py", line 187, in interaction self.cmdloop() File "/usr/lib/python2.5/cmd.py", line 130, in cmdloop line = raw_input(self.prompt) ValueError: I/O operation on closed file
The problem here is that processing closes the file descriptors for the processes it spawns, so a straight forward approach like that will not work. Due to the same reason using sys.__std(out|in|err)__ will not work.
The solution for me was to tell explicitly python to use my current stdin/stdout. The ‘r+’ flag is needed as pdb needs to read from stdin.
pdb.Pdb(stdin=open('/dev/stdin', 'r+'), stdout=open('/dev/stdout', 'r+')).set_trace()
I use this on Linux, AFAIK it should work across Unix world (and is probably horribly broken on Windows).
