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Title: Rewrite _reduce and _reconstructor in C
Type: enhancement Stage:
Components: Interpreter Core Versions: Python 2.6, Python 2.5
Status: closed Resolution: wont fix
Dependencies: Superseder:
Assigned To: gvanrossum Nosy List: alexandre.vassalotti, brett.cannon, gvanrossum, tim.peters
Priority: normal Keywords:

Created on 2002-09-25 18:15 by gvanrossum, last changed 2022-04-10 16:05 by admin. This issue is now closed.

Messages (7)
msg12478 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2002-09-25 18:15
The copy_reg defines two functions, _reduce() and
_reconstructor(), that are used for the pickling and
unpickling of new-style classes. These were originally
written in Python because the right implementation
wasn't entirely clear; _reduce() is actually called
from a C-level __reduce__ method defined in 'object',
and it references _reconstructor() in its return tuple.
It is now time to move both back into C for efficiency.
msg12479 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2002-11-14 16:46
Logged In: YES 

I'd like to add some comments from Jim Fulton on this (or a
related) issue so they don't get lost.

I still need to think of a good way to handle this. 
Currently, the pattern is a reduce return value of the form:

   reconstructor, (some_class, object, None), some_state

but there is a more general case where an uninitialized
object can be gotten by calling "type.__new__(some_class)",
or even: "some_class.__new__(some_class)".

There are really two issues:

- It's too hard to write __reduce__ functions for this case, and

- Too much data needs to be stored in pickles.

A new pickling code would handler the later, but I also want
to solve the former problem.

One thought is to return: (, (some_class, ),
some_state) where is:

   def new(class_): return class.__new__(class_)

The pickler could easily spot reduce returns with as the first value and generate a special
pickle code.
msg12480 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2003-02-12 22:19
Logged In: YES 

Lowering priority; when you use pickle protocol 2, none of
this Python code is used any more.

Jim's comment has been addressed by __newobj__ and
__getnewargs__ (see PEP 307).
msg12481 - (view) Author: Tim Peters (tim.peters) * (Python committer) Date: 2003-02-14 02:27
Logged In: YES 

Except that the new Python code _better_reduce() is used 
then.  As discussed, I intend to rewrite _reduce and 
_better_reduce in C, inside object's __reduce__ 
implementation, so I assigned this to me and boosted the 
priority.  I don't intend to recode _reconstructor in C, 
msg12482 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2003-02-19 22:38
Logged In: YES 

This isn't going to be done for 2.3a2; we'll revisit who
gets to do it closer to 2.3b1.
msg55903 - (view) Author: Brett Cannon (brett.cannon) * (Python committer) Date: 2007-09-13 23:54
Classifying as an RFE since this is not critical (as shown by it not
happening since early 2003).
msg59200 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2008-01-04 01:13
I just don't see this happening. Possibly it's out of date. Lots of
things have changed in the pickle world since 2002.
Date User Action Args
2022-04-10 16:05:42adminsetgithub: 37217
2008-01-04 01:13:17gvanrossumsetstatus: open -> closed
resolution: wont fix
messages: + msg59200
2008-01-04 00:43:58christian.heimessetversions: + Python 2.6, Python 2.5, - Python 2.3
2007-12-06 00:44:40alexandre.vassalottisetnosy: + alexandre.vassalotti
2007-09-13 23:54:29brett.cannonsettype: enhancement
messages: + msg55903
nosy: + brett.cannon
2002-09-25 18:15:01gvanrossumcreate