Re: pickle question: sequencing of operations
In article calwzidk3e353cnuuqpwr-4rromx7c9dbzapawurern9uzyu...@mail.gmail.com, Ian Kelly ian.g.ke...@gmail.com wrote: On Tue, May 8, 2012 at 1:19 PM, Russell E. Owen ro...@uw.edu wrote: In article rowen-df116b.12542704052...@news.gmane.org, Russell E. Owen ro...@uw.edu wrote: What is the sequence of calls when unpickling a class with __setstate__? I believe it just calls object.__new__ followed by yourclass.__setstate__. So at the point __setstate__ is called, you have a pristine instance of whatever class you're unpickling. I was wondering. I override __new__ (and __init__) to print messages and was quite surprised to only see __new__being called when the object was first created, not when it was being unpickled. But maybe there's something funny about my override that caused unpickle to ignore it and use the default version. I hope so. I can't see how the object could be constructed during unpickle without calling __new__. But that's one reason I was curious about the unpickling sequence of operations. -- Russell -- http://mail.python.org/mailman/listinfo/python-list
Re: pickle question: sequencing of operations
On Wed, May 9, 2012 at 1:39 PM, Russell E. Owen ro...@uw.edu wrote: I was wondering. I override __new__ (and __init__) to print messages and was quite surprised to only see __new__being called when the object was first created, not when it was being unpickled. But maybe there's something funny about my override that caused unpickle to ignore it and use the default version. I hope so. I can't see how the object could be constructed during unpickle without calling __new__. But that's one reason I was curious about the unpickling sequence of operations. You're probably pickling with the default protocol. Unpickling calls an overridden __new__ method only if the pickle protocol is at least 2. Using protocol 0 or 1, new-style class instances are constructed with the base object.__new__ instead. -- http://mail.python.org/mailman/listinfo/python-list
Re: pickle question: sequencing of operations
On Wed, May 9, 2012 at 2:34 PM, Ian Kelly ian.g.ke...@gmail.com wrote: On Wed, May 9, 2012 at 1:39 PM, Russell E. Owen ro...@uw.edu wrote: I was wondering. I override __new__ (and __init__) to print messages and was quite surprised to only see __new__being called when the object was first created, not when it was being unpickled. But maybe there's something funny about my override that caused unpickle to ignore it and use the default version. I hope so. I can't see how the object could be constructed during unpickle without calling __new__. But that's one reason I was curious about the unpickling sequence of operations. You're probably pickling with the default protocol. Unpickling calls an overridden __new__ method only if the pickle protocol is at least 2. Using protocol 0 or 1, new-style class instances are constructed with the base object.__new__ instead. BTW, in case you're wondering where all this is documented, pull up PEP 307 and read the sections Case 2 and Case 3. Cheers, Ian -- http://mail.python.org/mailman/listinfo/python-list
Re: pickle question: sequencing of operations
In article rowen-df116b.12542704052...@news.gmane.org, Russell E. Owen ro...@uw.edu wrote: What is the sequence of calls when unpickling a class with __setstate__? From experimentation I see that __setstate__ is called and __init__ is not, but I think I need more info. I'm trying to pickle an instance of a class that is a subclass of another class that contains unpickleable objects. What I'd like to do is basically just pickle the constructor parameters and then use those to reconstruct the object on unpickle, but I'm not sure how to go about this. Or an example if anyone has one. The following seems to work, but I don't know why: def __getstate__(self): ...return the argument dict needed for __init__ def __setstate__(self, argdict): self.__init__(**argdict) -- Russell -- http://mail.python.org/mailman/listinfo/python-list
Re: pickle question: sequencing of operations
On Tue, May 8, 2012 at 1:19 PM, Russell E. Owen ro...@uw.edu wrote: In article rowen-df116b.12542704052...@news.gmane.org, Russell E. Owen ro...@uw.edu wrote: What is the sequence of calls when unpickling a class with __setstate__? I believe it just calls object.__new__ followed by yourclass.__setstate__. So at the point __setstate__ is called, you have a pristine instance of whatever class you're unpickling. The following seems to work, but I don't know why: def __getstate__(self): ...return the argument dict needed for __init__ def __setstate__(self, argdict): self.__init__(**argdict) That seems like it should be fine as long as all your initialization code is in __init__ and not in __new__. Cheers, Ian -- http://mail.python.org/mailman/listinfo/python-list
pickle question: sequencing of operations
What is the sequence of calls when unpickling a class with __setstate__? From experimentation I see that __setstate__ is called and __init__ is not, but I think I need more info. I'm trying to pickle an instance of a class that is a subclass of another class that contains unpickleable objects. What I'd like to do is basically just pickle the constructor parameters and then use those to reconstruct the object on unpickle, but I'm not sure how to go about this. Or an example if anyone has one. -- Russell -- http://mail.python.org/mailman/listinfo/python-list
