Mailman 3 January 2008 - capi-sig

ANNOUNCE: PyBindGen 0.8
by Gustavo Carneiro March 11, 2022

March 11, 2022

The other day I released PyBindGen 0.8. Main news is that it features a new experimental header file scanner based on pygccxml (i.e., it's similar to py++ in scope, if not in maturity, but does not use boost.pythonunderneath). == What == PyBindGen is a Python module that is geared to generating C/C++ code that binds a C/C++ library for Python. It does so without extensive use of either C++ templates or C pre-processor macros. It has modular handling of C/C++ types, and can be easily extended with Python plugins. The generated code is almost as clean as what a human programmer would write, and does not depend on any library or header files besides Python itself. == Where == https://launchpad.net/pybindgen/ == NEWS == - Support C++ instance attributes through getter/setter methods - Support functions as methods of C++ classes - Support the PyObject* type - Support unsigned int, C strings (char*) (from Mark Lee) - Add basic support for enum types - New experimental automatic module generator based on C/C++ header file scanner and annotations in comments, using pygccxml - Some bug fixes -- Gustavo J. A. M. Carneiro INESC Porto, Telecommunications and Multimedia Unit "The universe is always one step beyond logic." -- Frank Herbert

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Register function to call at shutdown
by Hrvoje Niksic Jan. 19, 2008

Jan. 19, 2008

Is it possible to register a function to be called at finalization time? By finalization time I'm referring to the point at which Python is still operational, but is shutting down, for example the time when the modules are getting cleaned up. Functions registered with Py_AtExit get called too late, when it's no longer allowed to invoke any Python API function. I currently simulate this using an object whose __del__ invokes my function, and sticking that object in a private module. During module cleanup Python unhooks the object from the module, firing its __del__ which calls my function. But I consider it a hack, and a fragile one at that -- if anyone deletes the object from the module, the function will be called too early. I'd prefer a cleaner way to deal with this if possible.

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Question about proper GIL management for a language interoperability tool
by Tom Epperly Jan. 13, 2008

Jan. 13, 2008

I working on a language interoperability tool called Babel, https://computation.llnl.gov/casc/components/. It provides high-performance, bi-directional communication between any combination of C, C++, F77, F90, Java, and Python. Right now, I am trying to make sure I am handling the GIL locking and unlocking correctly, and I am wondering if the Python community can confirm whether I am handling things appropriately. Babel handles the many-to-many language interoperability problem with a hub and spoke architecture, so all inter-language calls go through C. Hence, I can discuss how I am handling the GIL in terms of communications between C and Python. I am going to describe what I am doing using pseudo-code and leaving out irrelevant details. CASE 1 (some other language calling Python via C) ======================================== foo_Factorial(struct foo_t *self, int32_t arg) { /* C routine that calls Python */ PyGILState_STATE _gstate; _gstate = PyGILState_Ensure(); /* convert incoming arguments from C to Python */ _result = PyObject_CallObject(_pfunc, _args); /* process outgoing arguments or exceptions */ PyGILState_Release(_gstate); /* return to caller in whatever language */ } CASE 2 (Python calling some other language via C) ======================================== static PyObject * pStub_foo_Factorial(PyObject *_self, PyObject *_args, PyObject *_kwdict) { PyObject *result; /* unpack incoming Python arguments into their C equivalents */ Py_BEGIN_ALLOW_THREADS /* dispatch to method implementation */ foo_Factorial(i,k,l); /* this step is actually done through a function pointer */ Py_END_ALLOW_THREADS /* pack outgoing C arguments into the Python return value or process any exceptions */ return result; } Discussion ======================================== Case 1 seems pretty straight forward. The current thread must own the GIL before making any Python C API calls, and it should release it when it's done. Case 2 also seems appropriate because function x_y_Method could very well do blocking I/O operation. For example, Babel also supports remote method invocation (RMI), so x_y_Method might dispatch the method across the network to another machine. In ceval.h where Py_BEGIN_ALLOW_THREADS and Py_END_ALLOW_THREADS are defined, it says "WARNING: NEVER NEST CALLS TO Py_BEGIN_ALLOW_THREADS AND Py_END_ALLOW_THREADS!!!". This makes me wonder if there is an issue with Python calling itself through Babel. Let's assume that Python is the main driver, and it calls a Babel wrapped Python method to calculate factorial or something. This will result in nested calls to PyGILState_Ensure/PyGILState_Release and Py_BEGIN_ALLOW_THREADS/Py_END_ALLOW_THREADS. Python interactive shell (invokes foo.Factorial(3)) Py_BEGIN_ALLOW_THREADS (in pStub_foo_Factorial (case 2)) PyGILState_Ensure (in foo_Factorial (case 1) arg=3) Py_BEGIN_ALLOW_THREADS (in pStub_foo_Factorial (case 2)) PyGILState_Ensure (in foo_Factorial (case 1) arg=2) Py_BEGIN_ALLOW_THREADS (in pStub_foo_Factorial (case 2)) PyGILState_Ensure (in foo_Factorial (case 1) arg=1) PyGILState_Release (in foo_Factorial (case 1) arg=1) Py_END_ALLOW_THREADS (in pStub_foo_Factorial (case 2)) PyGILState_Release (in foo_Factorial (case 1) arg=2) Py_END_ALLOW_THREADS (in pStub_foo_Factorial (case 2)) PyGILState_Release (in foo_Factorial (case 1) arg=3) Py_END_ALLOW_THREADS (in pStub_foo_Factorial (case 2)) Python interactive shell Is this approach correct? Regards, Tom Epperly LLNL/CASC

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Palm Vacations, A Travel Guide For Cologne
by Super Star Jan. 5, 2008

Jan. 5, 2008

Palm Vacations, A Travel Guide For Cologne Cologne is the four most populated cities in Germany. These days the city is a beautiful cultured destination with great leisure facilities, pubs and shops. However, during WWII, Cologne was heavily bombed and damaged. After years of restoration work it has been rebuilt to portray the wonderful historic Roman city it use to be. Travelling to Cologne Flying is the recommended choice of transport as the city has K?ln/Bonn Konrad Adenauer Airport located 10km from the centre. Also, for people arriving from countries that are outside Europe, Frankfurt Airport is the closest and provides transfers for the 200km journey. Trains and large roads make it easy to get to the city via other methods. Accommodation in Cologne Hotels are the most popular choice of accommodation in Cologne. However, check for the festival dates as this can seriously affect the availability of rooms. Hotels are great as they offer different classes of rooms and are conveniently situated around the city. A Brief History of Cologne Cologne has a vast history as it is the eldest city in Germany. The city has great importance in Roman History as it is one of four sanctified cities that formed the north corner spot of the Empire. At the beginning of the thirteenth century Cologne was renowned for being the largest fortified city in the world. However, it has been changed around a lot since then as 90% of Cologne was destroyed during WWII. City Attractions and Sights Since the heavy bombing in WWII, restoration efforts have seen the city burgeon into the historic Roman centre that it used to be. The Cologne Cathedral (K?lner Dom) that was originally established in 1248 was rebuilt to its previous state. It is an important feature of the city and one of the worlds most impressive Cathedrals. If you are interested in museums then head for the Aldstadt city?s most famous museums are such as the Museum Ludwig. For relaxation check out Claudius Spa that is found in the Rheinpark area although, you will need a car to make the journey. Shopping in Cologne Cologne has a great range of shops that cater for everybody?s needs. The most popular shopping areas are in the centre where there are a number of large. Other smaller streets that head out of the centre have more unique shops and indoor markets. The shopping areas are sectioned off for pedestrians, attractive and well laid out. Food and Drink Cologne has a great range of top quality restaurants that offer all kinds of international food. There are also numerous attractive cafes and bars as well as all takeaway options.

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Deploying embedded Python
by Andreas Raab Jan. 3, 2008

Jan. 3, 2008

Hi - I'm currently looking into a few deployment issues with our embedded Python interpreter and I'm looking for any information about deploying embedded Python that people may have. Specifically, I'm looking for the following information: 1) How to define a useful subset of the stdlib that can serve as an initial basis for the installation but later allows upgrade to the "full" library if desirable. In other words, I'd like to deploy a small subset of the stdlib to begin with (simply because of size constraints) which may later be extended to a full stdlib if this is desirable. Has someone done this before? I'd love to have a small "Python.zip" cross-platform stdlib surrogate that just gets shipped with the product. If not, what is the right starting point for analyzing the dependencies inside the stdlib? 2) How to isolate the embedded interpreter from environmental effects. I have found that on occasion, the interpreter would pick up "stray" installations which can cause weird problems. Which environmental settings affect the startup of an embedded Python interpreter? How does one work around/remove those dependencies? Is there any information available about how exactly the startup works? What is being read/loaded in which order etc? 3) General advice about deploying embedded Python. Pointers to web sites, general experience (good or bad) etc. are all very welcome. Thanks, - Andreas

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