I have a dll built in c++, under VS2010, and I am calling it from a python project.
I had an error, inside the dll, and I would have liked to be able to debug using VS tools, step into the solution until I reach the task that "read an invalid memory location". 
The debug / stepping into functions didn't step into the function code inside the dll. 
I tried to attach the debugger (and run the python code from command line/ stop at a raw_input that gave me the pid, then attach the debugger). Same thing happened. I hit the breakpoints inside the python code, but none inside the dll.
I eventually found my error, after much banging my head against my monitor, using old-style trace inside the dll. But there has to be a way to be able to debug an existing/ open project inside VS... I am going to run into this again, so I hope to learn something now, and avoid damage to my monitor in the future. :)
Note: the c++ dll and the pdb file are located both in the same directory as the python file, they are of course automatically built into the Debug folder, and they are also in a folder located into the system path. Any possible DEBUG symbols are enabled. I am using python 2.7.
You need to have the .pdb file in your bin directory if you want to be able to step into and debug a dll, otherwise you will not have access to any of the debugging symbols.  This .pdb allows visual studio to read the .dll file and step into its method calls.
debugging a c++ dll in VS2010, from python