ansaurus

Question

Method to peek at a Python program running right now

Answer 1

+4 A:

To "crash" a python program with a stacktrace you can send it SIGINT, that is unless you trap it or catch KeyboardInterrupt (python installs a SIGINT handler by default, that raises KeyboardInterrupt).

As for debugging, doesn't PyDev have built-in debugging support (through pdb)?

shylent 2009-10-28 13:32:13

Again, the program is running right now

Casebash 2009-10-28 21:17:05

which means you get the process id and do 'kill -INT $pid' . That will kill it, but should give you a stack trace. It does assume you have some way to see the stderr output.

Andrew Dalke 2009-10-28 22:28:18

Answer 2

+21 A:

If you place

import code
code.interact(local=locals())

at any point in your script, python will instantiate a python shell at exactly that point that has access to everything in the state of the script at that point. ^D exits the shell and resumes execution past that point.

You can even modify the state at that point from the shell, call functions, etc.

ʞɔıu 2009-10-28 13:35:40

Nice. I didn't know that (+1)

shylent 2009-10-28 13:36:47

Interesting. How does this differ from import pdb; pdb.set_trace( )?

Jon Hadley 2009-10-28 13:46:32

pdb gives you stepInto stepOut etc, etc and is its own special shell that you have to learn how to use that has step control over execution of the entire program. code.interact() is exactly the normal python shell that we all know and love. pdb is much more powerful and often overkill and difficult to use unless you know it well.

ʞɔıu 2009-10-28 13:56:42

Sorry for being unclear. I can't modify the script as it is already running

Casebash 2009-10-28 21:16:33

Your options for inspecting script execution (that I know of) are this thing, pdb or trace, but all of these require being able to modify the script. I don't think it's feasible while the script is running without modifying it.

ʞɔıu 2009-10-28 22:09:57

Answer 3

A:

Install signal handler that sets a trace function with sys.settrace() that prints traceback and clears clears trace function. This will allow you to see where your program is at any moment without interrupting it. Note, that signal is handled after each sys.getcheckinterval() python instructions.

Denis Otkidach 2009-10-28 13:48:53

Or have the signal handler set/unset the trace, so there's no overhead for the normal case.

Andrew Dalke 2009-10-28 20:22:27

Good point, I've updated the answer.

Denis Otkidach 2009-10-29 10:49:13

Answer 4

+2 A:

Personally, I prefer ipdb. It's pdb with added IPython goodness. It seems to be more of an interactive Python interpreter with a few shortcuts for debugging functions.

Walter 2009-10-28 14:20:24

Answer 5

+4 A:

If you have a running Python, which wasn't built with any sort of trace or logging mechanism, and you want to see what it's doing internally, then two options are:

On a Solaris or Mac, if you are using the system-provided Python then use dtrace
use gdb to attach to a running Python process,

Andrew Dalke 2009-10-28 20:33:20

Dtrace is awesome, unfortunately I am on Ubuntu

Casebash 2009-10-28 21:33:03

Answer 6

A:

If you're happy with a crash, inserting "1/0" will create a quick and dirty breakpoint, with a complete backtrace!

EOL 2009-10-28 20:50:16

ansaurus

tags:

views:

answers:

Method to peek at a Python program running right now

related questions