On 5/4/2011 12:51 PM, Daniel Neilson wrote:
Hello, I'm hoping that there will be someone here with sufficient expertise to answer a question on Python 3 for me. I work in the Computer Science department at a large Canadian University. We are currently doing a feasibility analysis for switching to using Python in our first year major-stream courses.
If you did, I believe you would be following in the footsteps of MIT.
Part of our first year curriculum requires that students be exposed to explicit dynamic memory allocation in the form of C++'s new/delete, C's malloc/free, etc. I realize that Python is garbage collected, and that there is never a need to explicitly allocate & deallocate objects. However, I am trying to determine whether or not it is possible to simulate that behaviour within Python via a module for the purposes of instruction.
The Python ctypes module allows one to invoke compiled C (or C++, I presume) functions in shared libraries (.dll on Windows, .so on *Nix).
For these purposes, I would like to know whether it is possible within Python 3 to write a Python-only module that, essentially, hooks into the "constructor" and "destructor" of many of the Python built-in types
Python is compiled as a small startup executable (<30 KB). The builtins are all in shared libraries that you can access with ctypes. The functions in those libraries are documented in the Python/C API manual.
(specifically list, dictionary, set, tuple, and string) so that the module can: 1) Maintain a list of object id()'s for objects that have been created. Ideally, this list would also contain the file & line number where the object was created. 2) Provide a "deallocate" function that will remove a given object's id() from the list from (1). 3) Print out an error message if the python script terminates with a non-empty list from (1). Preferably with a list of objects that are still "allocated."
I presume you can do all of this easily. For point 3, a script can register an 'atexit' function. As a sidenote, using ctypes 'allows' one to crash (segfault, bluescreen) a program just like when using C ;-). It thus voids the usual guarantee that one cannot do that.
Baring a Python-only module, would this behaviour be possible to add via a C-language module?
I do not think you will *need* to do this, though you might eventually decide to make a custom library with just the functions you want, with the names you want.
A module that hooked in to all memory allocation, and inspected the type of the object being allocated to conditionally add the object's id() to the list would also suffice. In either case, if such a module is possible, any pointers you could provide regarding how to implement such a module would be appreciated.
I hope the above helps. I think Python is a great learning language. -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
