Thomas Heller wrote:
Thomas Heller schrieb:
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.
It seems there isn't much interest in a patch - true?
No, I'm very interested in the patch. Thanks for it.
-Travis
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