On Monday 26 March 2007 12:43 pm, Robert Kern wrote: > Brian Blais wrote: > > Hello, > > > > I have a class defined in Pyrex (to get speed increases), and python > > complains that is can't be pickled (class def included below). I looked > > the documentation, and see that I can define __setstate__ and > > __getstate__ methods to pickle only certain methods/class variables. > > Unfortunately, I am not clear on which ones are causing the problem, so I > > figured I'd ask on the list before doing trial-and-error. I imagine it > > might be the "double *" , and perhaps the cdef methods, but I am not > > sure. > > There's no reliable way for the pickle machinery to introspect extension > type instances like it does pure Python instances. Consequently, I believe > that it simply throws up its hands unless if you have defined the > appropriate protocol methods. No particular attribute is causing a problem, > I don't think.
Here are some further remarks on how to define the appropriate protocol methods. In the SAGE codebase (http://www.sagemath.org), which contains well over 35,000 lines of Pyrex, we do a huge amount of pickling of Pyrex types. Long ago, after many many hours of frustration, I learned that there are two key things to keep in mind when pickling types defined using Pyrex: (1) Use the cPickle module with protocol 2, e.g., import cPickle cPickle.dumps(my_object, protocol=2) Using a different protocol, e.g., the default, is an exercise in suffering and frustration. (2) Define the __reduce__ method (setstate and getstate are for pure Python classes). Here's a typical example (for gmp integers, by the way): def __reduce__(self): # This is the *trick* needed to pickle pyrex extension types. # The trick is that you must put a pure Python function # as the first argument, and that function must return # the result of unpickling with the argument in the second # tuple as input. All kinds of problems happen # if we don't do this. return sage.rings.integer.make_integer, (self.str(32),) In this case, make_integer is (you have to see the relevant files to know what the Integer and PY_NEW things are, but they aren't really relevant): def make_integer(s): cdef Integer r r = PY_NEW(Integer) r._reduce_set(s) return r -- William --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://sage.scipy.org/sage/ and http://modular.math.washington.edu/sage/ -~----------~----~----~----~------~----~------~--~---
