Gabriel Genellina wrote: > En Mon, 08 Dec 2008 12:34:03 -0200, Cong Ma <[EMAIL PROTECTED]> escribió: > >> I'm writing a program that pickles an instance of a custom subclass of >> datetime.tzinfo. I followed the guides given in the Library Reference >> (version >> 2.5.2, chapter 5.1.6), which contain the note: >> >> "Special requirement for pickling: A tzinfo subclass must have an >> __init__ >> method that can be called with no arguments, else it can be pickled >> but possibly >> not unpickled again. This is a technical requirement that may be >> relaxed in the >> future." >> >> I tried this with an example "FixedOffset" subclass instance given in the >> Example section in the manual. It indeed failed to unpickle. To work >> around >> this, I found two possible solutions: >> 1. Modify the __init__ method so that it takes optional arguments with >> default >> values; > > Doing that still works with 2.6 and 3.0 > >> 2. Implement the __getinitargs__ method so that it does the opposite of >> __init__: returning a tuple from the instance's internal state that >> can be used >> to re-initialize an instance, retaining the old value. > > In fact, it doesn't matter *what* it returns, as far as they're valid > arguments to __init__ > >> My questions: >> 1. Is the "technical limitation" fixed in version 2.6 or 3.0? I can't >> check it >> for myself now... Python.org seems down and I can't find the docs. > > No, they behave the same (odd) way. > >> 2. To stick with version 2.5, which of the above 2 methods is better? >> Both seems >> to unpickle to the correct result, but are there subtle side-effects? >> Or there >> are better solutions? > > I'd use method 1, just because the __getinitargs__ are useless. >
Gabriel, Thank you so much for your great explanations. Had you not told me this, I would hardly be able to find it out by myself :) Regards, Cong. -- http://mail.python.org/mailman/listinfo/python-list
