Chan Kim Chan Kim - 1 year ago 100
Python Question

Debugging Python and C++ exposed by boost together

I can debug Python code using

ddd -pydb
. All the python command line arguments can be passed too after
. In my case, many classes have been implemented in C++ that are exposed to python using
. I wish I could debug python code and C++ together. For example I want to set break points like this :

break my_cpp.cpp:456

Of course I tried after compiling c++ codes with debug option but the debugger does not cross boost boundary. Is there any way?

I saw
I followed it and I can do debugging both for python and C++. But I preferably want to do visual debugging with
but I don't know how to give 'target exec python' command inside
. If not (just using
as in the link) I should be able to debug for a Python script not interactively giving python commands as in the link.

Answer Source

I found out how to debug the C++ part while running python. (while reading Python book..).
First you run the python program which includes C++ programs. At the start of the python program, use raw_input() to make the program wait for you input. But just before that do print os.getpid() (of course you should have imported os package). When you run the python program, it will have printed the pid of the python program you are running and will be waiting for your keyboard input.

python stop code :

import os

def w1(str):
    print (str)
    wait = raw_input()

print os.getpid()
w1('starting a key')

result :

starting a key

Or, you can use import pdb, pdb.set_trace() as comment below.(thanks @AndyG)

Now, suppose the C++ shared library is (which is my case. This library has all the C++ codes and boost python wrapper functions). 27352 is the pid. Then in another shell start gdb like

gdb caffe-fast-rcnn/python/caffe/ 27352

or if you want to use graphical debugging using like DDD, do

ddd caffe-fast-rcnn/python/caffe/ 27352

Then you'll see gdb starts and wait with prompt. The python program is interrupted by gdb and waits in stopped mode (it was waiting for your key input but now it's really in stopeed mode, and it needs gdb continue command from the second debugger to proceed with the key waiting).
Now you can give break point command in gdb like

br solver.cpp:225

and you can see message like

Breakpoint 1 at 0x7f2cccf70397: file src/caffe/solver.cpp, line 226. (2 locations)

When you give continue command in the second gdb window(that was holding the program), the python code runs again. Of course you should give a key input in the first gdb window to make it proceed.
Now at least you can debug the C++ code while running python program(that's what I wanted to do)!

I later checked if I can do python and C++ debugging at the same time and it works. You start the debugger(DDD) like ddd -pydb options.. and attach another DDD using method explained above. Now you can set breakpoints for python and C++ and using other debug functions in each window(I wish I had known this a couple of months earlier.. I should have helped tons.).

enter image description here

EDIT : to get the pid, you can do ps -aux | grep python instead. This pid is the next of ddd's pid.

Recommended from our users: Dynamic Network Monitoring from WhatsUp Gold from IPSwitch. Free Download