[Python-Dev] Accepting PEP 3154 for 3.4?

Alexandre Vassalotti alexandre at peadrop.com
Wed Nov 20 09:40:38 CET 2013

On Tue, Nov 19, 2013 at 2:09 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> Well, I don't think it's a big deal to add a FRAME opcode if it doesn't
> change the current framing logic. I'd like to defer to Alexandre on this
> one, anyway.

Looking at the different options available to us:

1A. Mandatory framing
      (+) Allows the internal buffering layer of the Unpickler to rely
          on the presence of framing to simplify its implementation.
      (-) Forces all implementations of pickle to include support for
          framing if they want to use the new protocol.
      (-) Cannot be removed from future versions of the Unpickler
          without breaking protocols which mandates framing.
1B. Optional framing
      (+) Could allow optimizations to disable framing if beneficial
          (e.g., when pickling to and unpickling from a string).

2A. With explicit FRAME opcode
      (+) Makes optional framing simpler to implement.
      (+) Makes variable-length encoding of the frame size simpler
          to implement.
      (+) Makes framing visible to pickletools.
      (-) Adds an extra byte of overhead to each frames.
2B. No opcode

3A. With fixed 8-bytes headers
     (+) Is simple to implement
     (-) Adds overhead to small pickles.
3B. With variable-length headers
     (-) Requires Pickler implemention to do extra data copies when
         pickling to strings.

4A. Framing baked-in the pickle protocol
     (+) Enables faster implementations
4B. Framing through a specialized I/O buffering layer
     (+) Could be reused by other modules

I may change my mind as I work on the implementation, but at least for now,
I think the combination of 1B, 2A, 3A, 4A will be a reasonable compromise
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