Can't deepcopy bytes-derived class

[Dan]

On Dec 8, 9:05 pm, Terry Reedy <tjre... at udel.edu> wrote:
> On 12/8/2010 7:11 PM, Ned Deily wrote:
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> > In article<idosir$45... at dough.gmane.org>, Terry
> > Reedy<tjre... at udel.edu>  wrote:
> >> On 12/8/2010 2:42 PM, Dan wrote:
> >>> I have a simple type derived from bytes...
>
> >>> class atom(bytes): pass
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> >>> ... that I cannot deepcopy().  The session below demonstrates
> >>> how deepcopy() of "bytes" works fine, but deepcopy() of "atom"
> >>> does not.
> > [...]
> >>> Python 3.1.2 (r312:79149, Mar 21 2010, 00:41:52) [MSC v.1500 32
> >>> bit (Intel)] Type "help", "copyright", "credits" or "license" for
> >>> more information.
> >>>>>> import copy class atom(bytes):
> >>> ...        pass ...
> >>>>>> copy.deepcopy(b'abc')
> >>> b'abc'
> >>>>>> copy.deepcopy(atom(b'abc'))
> >>> Traceback (most recent call last): File "C:\Program Files
> >>> (x86)\Wing IDE 3.2\src\debug\tserver \_sandbox.py", line 1,
> >>> in<module> # Used internally for debug sandbox under external
> >>> interpreter File "C:\Python31\Lib\copy.py", line 173, in
> >>> deepcopy y = _reconstruct(x, rv, 1, memo) File
> >>> "C:\Python31\Lib\copy.py", line 280, in _reconstruct y =
> >>> callable(*args) File "C:\Python31\Lib\copyreg.py", line 88, in
> >>> __newobj__ return cls.__new__(cls, *args) builtins.TypeError:
> >>> string argument without an encoding
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> >> You could trace through copy.py and copyreg.py to see where bytes
> >> and atom get treated differently.
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> >> This might be a bug that should be reported on the tracker, but I
> >> do not know. Let see what anyone else says.
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> > FWIW, the example still fails with Python 3.1.3 but seems to work OK
> > with a recent alpha build of Python 3.2.  What specific change might
> > have fixed it doesn't come immediately to mind.
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> According to difflib.unified_diff, the only difference between
> Lib/copy.py from 3.1 to 3.2 is 4 lines:
> +
> +def _deepcopy_method(x, memo): # Copy instance methods
> +    return type(x)(x.__func__, deepcopy(x.__self__, memo))
> +_deepcopy_dispatch[types.MethodType] = _deepcopy_method
>
> (and none in copyreg.py)
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> These were added in rev76572 as part ofhttp://bugs.python.org/issue1515
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> Guido decreed this to be a new feature rather than bugfix, so the change
> went into future 2.7 and 3.2 and not existing 2.6 and 3.1.
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> Tto verify that these cause the change, comment out in 3.2 or add to
> 3.1. I have not read through the issue to understand it or why it would
> affect the OP's code case.
>
> --
> Terry Jan Reedy

Thank you everyone.  Knowing that it works in 3.2 is good enough for
me.

I tested the 4 line change anyway...removing it from 3.2 had no
detrimental effect, adding it to 3.1 had no effect.  It must be
something else.

Regards,
Dan.