> Sturla Molden schrieb: >> On 3/26/2009 12:41 PM, Jens Rantil wrote: >> >>> Wouldn't my code, or a tweak of it, be a nice feature in >>> numpy.ctypeslib? Is this the wrong channel for proposing things like >>> this? >> >> If you look at >> >> http://svn.scipy.org/svn/numpy/trunk/numpy/ctypeslib.py >> >> you will see that it does almost the same. I think it would be better to >> work out why ndpointer fails as restype and patch that. >
Thomas Heller schrieb: > ndpointer(...), which returns an _nptr instance, does not work as restype > because neither it is a base class of one of the ctypes base types like > ctypes.c_void_p, also it is not callable with one argument. > > There are two ways to fix this. The first one is to make the _nptr callable [...] > > The other way is to make _nptr a subclass of ctypes.c_void_p, > the result that the foreign function call returns will then be > an instance of this class. Unfortunately, ctypes will not call > __new__() to create this instance; so a custom __new__() implementation > cannot return a numpy array and we are left with the _nptr instance. > The only way to create and access the numpy array is to construct > and return one from a method call on the _nptr instance, or a property > on the _nptr instance. > Ok, .errcheck could call that method and return the result. > Well, looking into the ctypes sources trying to invent a new protocol for the restype attribute I found out that THERE IS ALREADY a mechanism for it, but I had totally forgotten that it exists. When the .restype attribute of a function is set to a SUBCLASS of a ctypes type (c_void_p for example), an instance of this subclass is created. After that, if this instance has a _check_retval_ method, this method is called and the result of this call is returned. So, it is indeed possible to create a class that can be assigned to .restype, and which can convert the return value of a function to whatever we like. I will prepare a patch for numpy.ctypeslib. -- Thanks, Thomas _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
