Mailman 3 November 2012 - capi-sig

ANN: expy 0.6.5 released!
by Yingjie Lan April 16, 2022

April 16, 2022

EXPY is an express way to extend Python! EXPY provides a way to extend python in an elegant way. For more information and a tutorial, see: http://expy.sourceforge.net/ What's new: 1. Correct treatment of __init__ method. 2. Give warnings of missing Py_INCREF on appropriate special type methods. 3. Documentation update. Cheers, Yingjie

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ANNOUNCE: PyBindGen 0.8
by Gustavo Carneiro March 10, 2022

March 10, 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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C API equivalent to abc.ABCMeta.register?
by Daniel Stutzbach March 2, 2022

March 2, 2022

I'm the author of an extension module (blist) that provides a type that fits the MutableSequence API. Is there a canonical way for me to register the type as a MutableSequence from the C API? -- Daniel Stutzbach, Ph.D. President, Stutzbach Enterprises, LLC <http://stutzbachenterprises.com>

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Software Development - Application Development - Game Development
by Gary Jan. 10, 2022

Jan. 10, 2022

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Re: [capi-sig] What's up with PyTypeObject and functions?
by M.-A. Lemburg Nov. 28, 2012

Nov. 28, 2012

On 28.11.2012 04:01, Robert Steckroth wrote: > Hey Gang, why is the below snippet for error checking not working? I wan't > to be able to pass in different PyTypeObjects > to the CHECK_TYPE function and check an object for that type. > It works fine when I insert put &PyString_Type directly into > the function like so --> > if ( ! PyObject_TypeCheck(s_obj, &PyString_type) ) > However, the CHECK_TYPE function will return -1 if I pass the PyTypeObject > in, like at the bottom of this message. > Why does PyObject_TypeCheck not work if PyTypeObject is first passed into a > function? > > > int CHECK_TYPE(PyObject *s_obj, PyTypeObject obj_type) { You need *obj_type here, since you need the pointer to the object, not the object itself. > if ( ! s_obj ) > return 1; > > if ( ! PyObject_TypeCheck(s_obj, &obj_type) ) { This needs to be obj_type. Your code will pass in the address of the PyTypeObject on the stack, which will not match any of the type objects in the Python type system. > PyErr_Format(PyExc_TypeError, "[ %s ] object needs to be of > type [ %s ]\n\nUsage: %s", PyString_AsString(PyObject_Repr(s_obj)), > obj_type.tp_name, obj_type.tp_doc ); This code leaks memory since the representation object is not freed. > return -1; } > > return 1; > > } > > if ( !CHECK_TYPE(align, PyString_Type) ) return NULL; This needs to the &PyString_Type -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Nov 28 2012) >>> Python Projects, Consulting and Support ... http://www.egenix.com/ >>> mxODBC.Zope/Plone.Database.Adapter ... http://zope.egenix.com/ >>> mxODBC, mxDateTime, mxTextTools ... http://python.egenix.com/ ________________________________________________________________________ ::: Try our new mxODBC.Connect Python Database Interface for free ! :::: eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg Registered at Amtsgericht Duesseldorf: HRB 46611 http://www.egenix.com/company/contact/

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What's up with PyTypeObject and functions?
by Robert Steckroth Nov. 28, 2012

Nov. 28, 2012

Hey Gang, why is the below snippet for error checking not working? I wan't to be able to pass in different PyTypeObjects to the CHECK_TYPE function and check an object for that type. It works fine when I insert put &PyString_Type directly into the function like so --> if ( ! PyObject_TypeCheck(s_obj, &PyString_type) ) However, the CHECK_TYPE function will return -1 if I pass the PyTypeObject in, like at the bottom of this message. Why does PyObject_TypeCheck not work if PyTypeObject is first passed into a function? int CHECK_TYPE(PyObject *s_obj, PyTypeObject obj_type) { if ( ! s_obj ) return 1; if ( ! PyObject_TypeCheck(s_obj, &obj_type) ) { PyErr_Format(PyExc_TypeError, "[ %s ] object needs to be of type [ %s ]\n\nUsage: %s", PyString_AsString(PyObject_Repr(s_obj)), obj_type.tp_name, obj_type.tp_doc ); return -1; } return 1; } if ( !CHECK_TYPE(align, PyString_Type) ) return NULL; -- Bust0ut, Surgemcgee: Systems Engineer --- surgemcgee.com Django_Teamplate3d

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Re: [capi-sig] Best practice for object attribute use in other objects...
by Stefan Behnel Nov. 23, 2012

Nov. 23, 2012

Robert Steckroth, 23.11.2012 17:26: > Hey Gang, I am using object attributes from other objects in my module. Can > anyone tell me the best way to retrieve the object attributes without > un-necessary overhead? Is it better to simply call > a PyObject_GetAttrString(My_object, "width")? You should read the source. It will create an intermediate Python object for the attribute name. > Does it create un-necessary overhead to declare the object in the head of > the function as so? > > My_object *m_obj; > w = m_obj->width; If the field you are accessing is a C field in an extension type, then yes, that's the way to do it. This is a straight C pointer dereference that is way more efficient than a dict lookup of a Python attribute and the packing or unpacking of a Python object value that tends to go with it. > Also, would I need to --> Py_XDECREF(m_obj) at the end of the function if > this is a "clean" way of doing it? Depends on where you got the value from. If you own the reference, you have to decref it at the end, yes. > Is there any performance concerns between the two? Not unless your code is performance critical. If it is, you will prefer the direct pointer dereference. Otherwise, you don't have to care. In any case, you should first write your code, then benchmark it, then see if it's fast enough or if it needs improvements and/or optimisation. C code is not Python code. It's way harder to write and to get right. So a) avoid writing it in the first place and b) if you find that you really have to, write as little of it as possible and avoid premature optimisations on the way. I keep repeating myself, but there are tools that take care of all of the above for you automatically. Stefan

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Best practice for object attribute use in other objects...
by Robert Steckroth Nov. 23, 2012

Nov. 23, 2012

Hey Gang, I am using object attributes from other objects in my module. Can anyone tell me the best way to retrieve the object attributes without un-necessary overhead? Is it better to simply call a PyObject_GetAttrString(My_object, "width")? Does it create un-necessary overhead to declare the object in the head of the function as so? > My_object *m_obj; w = m_obj->width; Also, would I need to --> Py_XDECREF(m_obj) at the end of the function if this is a "clean" way of doing it? Is there any performance concerns between the two? -- Bust0ut, Surgemcgee: Systems Engineer --- surgemcgee.com Django_Teamplate3d

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Re: [capi-sig] expression as argument of a object
by Stefan Behnel Nov. 22, 2012

Nov. 22, 2012

nirmoy das, 21.11.2012 12:38: > Can anyone tell me how to use expression in PyObject_CallObject() > as argument of object > > ex:column_family('keyspace', 'CF', comparator_type=comparator) My (biased) advice is to use Cython. It allows you to call functions in plain and simple Python syntax, including keyword arguments and the like. So your example above completely solves your problem already. If you want to do it manually, and assuming that with "expression" you mean "keyword arguments", as in your example above, you have to first build a dict with PyDict_New(), then add a new value to it, then pass the dict into the call, and then decref the reference to the dict. Stefan

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Re: [capi-sig] expression as argument of a object
by Hrvoje Niksic Nov. 22, 2012

Nov. 22, 2012

nirmoy das <nirmoy.aiemd(a)gmail.com> writes: > ex:column_family('keyspace', 'CF', comparator_type=comparator) You cannot use PyObject_CallObject to pass keyword arguments to a function; use PyObject_Call. The easiest way is to use Py_BuildValue to create the positional and the keyword arguments. For example: /* error checking omitted for brevity */ PyObject *args, *kwds, *ret; args = Py_BuildValue("ss", "keyspace", "CF"); kwds = Py_BuildValue("sO", "comparator_type", comparator"); ret = PyObject_Call(column_family, args, kwds) Py_DECREF(args); Py_DECREF(kwds);

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