On Apr 5, 2011, at 12:58 PM, John Ladasky wrote: > Hi Philip, > > Thanks for the reply. > > On Apr 4, 4:34 pm, Philip Semanchuk <phi...@semanchuk.com> wrote: >> So if you're going to use multiprocessing, you're going to use pickle, and >> you >> need pickleable objects. > > OK, that's good to know.
But as Dan Stromberg pointed out, there are some pickle-free ways to communicate between processes using multiprocessing. > This leads straight into my second question. I THINK, without knowing > for sure, that most user classes would pickle correctly by simply > iterating through __dict__. So, why isn't this the default behavior > for Python? Was the assumption that programmers would only want to > pickle built-in classes? One can pickle user-defined classes: >>> class Foo(object): ... pass ... >>> import pickle >>> foo_instance = Foo() >>> pickle.dumps(foo_instance) 'ccopy_reg\n_reconstructor\np0\n(c__main__\nFoo\np1\nc__builtin__\nobject\np2\nNtp3\nRp4\n.' And as Robert Kern pointed out, numpy arrays are also pickle-able. >>> import numpy >>> pickle.dumps(numpy.zeros(3)) "cnumpy.core.multiarray\n_reconstruct\np0\n(cnumpy\nndarray\np1\n(I0\ntp2\nS'b'\np3\ntp4\nRp5\n(I1\n(I3\ntp6\ncnumpy\ndtype\np7\n(S'f8'\np8\nI0\nI1\ntp9\nRp10\n(I3\nS'<'\np11\nNNNI-1\nI-1\nI0\ntp12\nbI00\nS'\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00'\np13\ntp14\nb." As a side note, you should always use "new style" classes, particularly since you're exploring the details of Python class construction. "New" is a bit a of misnomer now, as "new" style classes were introduced in Python 2.2. They have been the status quo in Python 2.x for a while now and are the only choice in Python 3.x. Subclassing object gives you a new style class: class Foo(object): Not subclassing object (as you did in your example) gives you an old style class: class Foo: Cheers Philip -- http://mail.python.org/mailman/listinfo/python-list
