John Reid wrote:
John Reid wrote:
Ralf W. Grosse-Kunstleve wrote:
Ok I'll give that a whirl. I was hoping to avoid doing
__getinitargs__()
for each subclass as I have quite a few of them. If I didn't have a C++
base class then the pickling would just work as is. There's no way I
can get back to that sort of situation with the C++ base class is
there?
I don't know, but there may be. One (totally untested) idea would be to
give the base class __getstate__ and __setstate__ methods that
inspect the
instance to re/store the state. Maybe you just need to return and
restore
self.__dict__?
I guess you could mix-in the __getstate__, __setstate__ methods.
Ralf
I'm not sure what you mean by mix-in, but my first attempt involved
defining pickle suite getstate() and setstate() methods. I did not
define a getinitargs() method. Unfortunately when the derived object
was unpickled, __init__ was called with no arguments. As far as I can
see there's no way to use the boost.python pickle suite that does not
involve a call to __init__() on the unpickled object.
I'll try having a go using the python pickling protocol's __reduce__()
method.
Ok this seems to work by injecting a __reduce__() method into the C++
base class. Here ext is the extension module and A is the C++ base class:
import ext, cPickle, logging, copy_reg
def __newobj__(cls, *args):
return cls.__new__(cls, *args)
def __reduce__(self):
return (
__newobj__,
(self.__class__,),
self.__dict__
)
ext.A.__reduce__ = __reduce__
class Derived(ext.A):
def __init__(self, init_arg):
self.data = init_arg
derived = Derived(1)
pickled_repr = cPickle.dumps(derived)
unpickled = cPickle.loads(pickled_repr)
assert unpickled.data == derived.data
OK it seems I was a bit optimistic. When I pass an unpickled object back
to C++, I get this error:
Boost.Python.ArgumentError: Python argument types in
ext.method_that_takes_A(Derived)
did not match C++ signature:
method_that_takes_A(A)
Does anyone have any ideas why my solution doesn't work when I try to
pass an unpickled object back to C++? I guess I need to learn a bit more
about how __new__() works.
John.
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