Alexander Belopolsky <alexander.belopol...@gmail.com> writes: > No credit for anything other than the "extra credit" section. Partial > credit for that. Study that printout and you should understand what > Tim was saying.
My original claim was that the pickler can't know and doesn't care if a byte string value merely happens to be 10 bytes long for this object, or is 10 bytes long every time, it will encode it with SHORT_BINBYTES ["C", count of bytes, string of bytes] regardless. The datetime constructor itself does care what value is passed to it, but what I was saying was the class could have been written originally to accept optionally longer strings and ignore the extra values, so that future versions could pickle as longer strings and be compatible. In such a case, the actual pickle format would _still_ have consisted of __reduce__() == (datetime, (b"..........", [optional tzinfo])), just with the option of accepting (and ignoring) longer byte strings encoded by later versions of the datetime class. The pickle format is versatile enough to pass any (pickleable) value at all to a constructor (or to __setstate__). Designing the datetime constructor/setstate in the past to be able to accept a byte string of a length other than exactly 10 would have allowed the representation to be extended in the present, rather than smuggling a single extra bit into one of the existing bytes. But it would not have changed the actual representation that would have been produced by pickle back then, not one bit. And, now, to answer my own question from a previous message... >>> class C(): ... def __reduce__(self): ... return (datetime, (b"\x07\xdf\t\x0e\x155'\rA\xb2",)) ... >>> pickle.loads(pickle.dumps(C())) datetime.datetime(2015, 9, 14, 21, 53, 39, 868786) >>> class C(): ... def __reduce__(self): ... return (datetime, (b"\x07\xdf\t\x0e\x955'\rA\xb2",)) ... >>> pickle.loads(pickle.dumps(C())) datetime.datetime(2015, 9, 14, 149, 53, 39, 868786) >>> datetime.strftime(pickle.loads(pickle.dumps(C())), '%Y%m%d%H%M%S') Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: hour out of range That was the bit we were talking about, right? -- https://mail.python.org/mailman/listinfo/python-list
