Question

I would need to run a python script for some random amount of time, pause it, get a stack traceback, and unpause it. I’ve googled around for a way to do this, but I see no obvious solution.

Answer 1

There’s the statprof module

pip install statprof (or easy_install statprof), then to use:

import statprof

statprof.start()
try:
    my_questionable_function()
finally:
    statprof.stop()
    statprof.display()

There’s a bit of background on the module from this blog post:

Why would this matter, though? Python already has two built-in profilers: lsprof and the long-deprecated hotshot. The trouble with lsprof is that it only tracks function calls. If you have a few hot loops within a function, lsprof is nearly worthless for figuring out which ones are actually important.

A few days ago, I found myself in exactly the situation in which lsprof fails: it was telling me that I had a hot function, but the function was unfamiliar to me, and long enough that it wasn’t immediately obvious where the problem was.

After a bit of begging on Twitter and Google+, someone pointed me at statprof. But there was a problem: although it was doing statistical sampling (yay!), it was only tracking the first line of a function when sampling (wtf!?). So I fixed that, spiffed up the documentation, and now it’s both usable and not misleading. Here’s an example of its output, locating the offending line in that hot function more accurately:

  %   cumulative      self          
 time    seconds   seconds  name    
 68.75      0.14      0.14  scmutil.py:546:revrange
  6.25      0.01      0.01  cmdutil.py:1006:walkchangerevs
  6.25      0.01      0.01  revlog.py:241:__init__
  [...blah blah blah...]
  0.00      0.01      0.00  util.py:237:__get__
---
Sample count: 16
Total time: 0.200000 seconds

I have uploaded statprof to the Python package index, so it’s almost trivial to install: “easy_install statprof” and you’re up and running.

Since the code is up on github, please feel welcome to contribute bug reports and improvements. Enjoy!