[New-bugs-announce] [issue22783] Pickle: use NEWOBJ instead of NEWOBJ_EX if possible

[Serhiy Storchaka]

New submission from Serhiy Storchaka:

Currently in pickle with protocol 4 the NEWOBJ_EX opcode is used to reconstruct objects with __getnewargs__() or __getnewargs_ex__() even if there no keyword arguments.

>>> import pickle, pickletools, collections
>>> P = collections.namedtuple('P', 'x y')
>>> pickletools.dis(pickle.dumps(P(12, 34), 3))
    0: \x80 PROTO      3
    2: c    GLOBAL     '__main__ P'
   14: q    BINPUT     0
   16: K    BININT1    12
   18: K    BININT1    34
   20: \x86 TUPLE2
   21: q    BINPUT     1
   23: \x81 NEWOBJ
   24: q    BINPUT     2
   26: .    STOP
highest protocol among opcodes = 2
>>> pickletools.dis(pickle.dumps(P(12, 34), 4))
    0: \x80 PROTO      4
    2: \x95 FRAME      28
   11: \x8c SHORT_BINUNICODE '__main__'
   21: \x94 MEMOIZE
   22: \x8c SHORT_BINUNICODE 'P'
   25: \x94 MEMOIZE
   26: \x93 STACK_GLOBAL
   27: \x94 MEMOIZE
   28: K    BININT1    12
   30: K    BININT1    34
   32: \x86 TUPLE2
   33: \x94 MEMOIZE
   34: }    EMPTY_DICT
   35: \x94 MEMOIZE
   36: \x92 NEWOBJ_EX
   37: \x94 MEMOIZE
   38: .    STOP
highest protocol among opcodes = 4

These EMPTY_DICT//MEMOIZE//NEWOBJ_EX can be replaced by single NEWOBJ. Actually there is a regression in protocol 4 against protocol 3, so may be following patch should be applied on 3.4 too.

Here is a patch which uses __newobj__ instead of __newobj_ex__ if there are no keywords arguments. Also it reduce the number of lines of C code and adds tests for classes with __getnewargs__() and __getnewargs_ex__().

----------
components: Library (Lib)
files: pickle_newobj.patch
keywords: patch
messages: 230490
nosy: alexandre.vassalotti, pitrou, serhiy.storchaka
priority: normal
severity: normal
stage: patch review
status: open
title: Pickle: use NEWOBJ instead of NEWOBJ_EX if possible
type: enhancement
versions: Python 3.5
Added file: http://bugs.python.org/file37107/pickle_newobj.patch

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue22783>
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