Alexander Belopolsky <[email protected]> added the comment:
OK, the 2.7 behavior is explainable and correct. cPickle checks the reference
count and does not generate PUT for objects that don't have references:
>>> from pickletools import dis
>>> from cPickle import dumps
>>> dis(dumps(tuple([1])))
0: ( MARK
1: I INT 1
4: t TUPLE (MARK at 0)
5: . STOP
highest protocol among opcodes = 0
>>> t = 1,
>>> dis(dumps(t))
0: ( MARK
1: I INT 1
4: t TUPLE (MARK at 0)
5: p PUT 1
8: . STOP
highest protocol among opcodes = 0
This optimization is not available from python, of course so pickle.py behaves
differently.
The remaining question is why this optimization was removed from 3.x.
----------
versions: +Python 3.2 -Python 2.7
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<http://bugs.python.org/issue8738>
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