eryksun added the comment:
> Packages do this because it's the natural thing to do
I guess the tutorial is channeling projects toward using the cdll/windll
LibraryLoader instances on Windows. It even shows using
cdll.LoadLibrary('libc.so.6') on Linux. That's equivalent to CDLL('libc.so.6');
I don't know why one would bother with cdll.LoadLibrary.
> there's not even a notion they _need_ to be cloned.
The ctypes reference has always explained how CDLL instances cache function
pointers via __getattr__ and (formerly) __getitem__.
The same section also documents that LibraryLoader.__getattr__ caches
libraries. However, it's missing an explanation of LibraryLoader.__getitem__,
which returns getattr(self, name), for use when the library name isn't a valid
Python identifier.
> there's no apparent way to clone a pointer
You can use pointer casting or from_buffer_copy to create a new function
pointer. It isn't a clone because it only uses the function pointer type, not
the current value of restype, argtypes, and errcheck. But this may be all you
need. For example:
>>> from ctypes import *
>>> libm = CDLL('libm.so.6')
cast:
>>> sin = cast(libm.sin, CFUNCTYPE(c_double, c_double))
>>> sin(3.14/2)
0.9999996829318346
>>> sin2 = cast(sin, type(sin))
>>> sin2.argtypes
(<class 'ctypes.c_double'>,)
>>> sin2.restype
<class 'ctypes.c_double'>
from_buffer_copy:
>>> sin = CFUNCTYPE(c_double, c_double).from_buffer_copy(libm.sin)
>>> sin(3.14/2)
0.9999996829318346
https://docs.python.org/3/library/ctypes.html#ctypes.cast
https://docs.python.org/3/library/ctypes.html#function-prototypes
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<http://bugs.python.org/issue22552>
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