How to get a stack trace from a stuck/hanging python script

how-to.md

How to get a stack trace for each thread in a running python script

Sometimes a python script will simply hang forever with no indication of where things went wrong. Perhaps it's polling a service that will never return a value that allows the program to move forward. Here's a way to see where the program is currently stuck.

Install gdb and pyrasite

Install gdb.

# Redhat, CentOS, etc
$ yum install gdb

# Ubuntu, Debian, etc
$ apt-get update && apt-get install gdb

# MacOS
$ brew install gdb

Install pyrasite.

$ pip install pyrasite

Inspect process with pyrasite

Find the process ID for the stuck python process and run pyrasite-shell with it.

# Assuming process ID is 12345
$ pyrasite-shell 12345

You should now see a python REPL. Run the following in the REPL to see stack traces for all threads.

from __future__ import print_function

import sys, traceback

for thread_id, frame in sys._current_frames().items():
    print('Stack for thread {}'.format(thread_id))
    traceback.print_stack(frame)
    print('')

python 3 version

import sys, traceback

for thread_id, frame in sys._current_frames().items():
    print('Stack for thread {}'.format(thread_id))
    traceback.print_stack(frame)
    print('')

I've adapted this gist to Python 3 (and some additional tweaks): https://gist.github.com/soxofaan/58ae2e266b63a2471a1f1b49a133bac9