[issue22890] StringIO.StringIO pickled in 2.7 is not unpickleable on 3.x

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

There is the _compat_pickle module that purposed to support backward and 
forward compatibility for renamed or moved classes and modules.

StringIO.StringIO in 2.x corresponds to io.StringIO or io.BytesIO. The problem 
is that we can't determine what of classes is a match in every concrete case, 
especially if StringIO.StringIO is empty.

But since cStringIO.StringIO is not pickleable either, I now think that it is 
not worth to support to support compatibility with pickled StringIO.StringIO 
instances.

--
resolution:  -> wont fix
stage:  -> resolved
status: open -> closed

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[issue22890] StringIO.StringIO pickled in 2.7 is not unpickleable on 3.x

[Mark Lawrence]

Changes by Mark Lawrence :


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nosy:  -BreamoreBoy

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[issue22890] StringIO.StringIO pickled in 2.7 is not unpickleable on 3.x

[Jelle Zijlstra]

Jelle Zijlstra added the comment:

Unless I'm missing something, StringIO doesn't exist as a module in Python 3, 
as mentioned in 
https://docs.python.org/3.0/whatsnew/3.0.html#text-vs-data-instead-of-unicode-vs-8-bit.

If you're trying to unpickle in 3.x an object pickled by 2.7.x, I'm not sure 
there is a guarantee that unpickling works for objects in modules that were 
renamed between 2.x and 3.x. This also doesn't work if you pickle a 
ConfigParser in 2.7 and unpickle it in 3.x.

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[issue22890] StringIO.StringIO pickled in 2.7 is not unpickleable on 3.x

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

The issue is about StringIO.StringIO, not io.StringIO.

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[issue22890] StringIO.StringIO pickled in 2.7 is not unpickleable on 3.x

[Mark Lawrence]

Mark Lawrence added the comment:

Seems fine on Windows 8.1

c:\Users\Mark\Documents\MyPythonc:\cpython\PCbuild\amd64\python.exe
Python 3.5.0a1+ (default:344d57c521b9+, Feb 27 2015, 13:39:56) [MSC v.1800 64 
bit (AMD64)] on win32
Type help, copyright, credits or license for more information.
 import pickle, io
 pickle.dumps(io.StringIO('abc'), 2)
b'\x80\x02c_io\nStringIO\nq\x00)\x81q\x01(X\x03\x00\x00\x00abcq\x02X\x01\x00\x00\x00\nq\x03K\x00Ntq\x04b.'
 pickle.loads(b'\x80\x02c_io\nStringIO\nq\x00)\x81q\x01(X\x03\x00\x00\x00abcq\x02X\x01\x00\x00\x00\nq\x03K\x00Ntq\x04b.')
_io.StringIO object at 0x004C6E604288


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[issue22890] StringIO.StringIO pickled in 2.7 is not unpickleable on 3.x

[Serhiy Storchaka]

New submission from Serhiy Storchaka:

StringIO.StringIO is pickleable and unpickleable on 2.7 but is not unpickleable 
on 3.x.

Python 2.7:
 import pickle, StringIO
 pickle.dumps(StringIO.StringIO('abc'), 2)
'\x80\x02(cStringIO\nStringIO\nq\x00oq\x01}q\x02(U\tsoftspaceq\x03K\x00U\x07buflistq\x04]q\x05U\x03posq\x06K\x00U\x03lenq\x07K\x03U\x06closedq\x08\x89U\x03bufq\tU\x03abcq\nub.'
 pickle.loads(b'\x80\x02(cStringIO\nStringIO\nq\x00oq\x01}q\x02(U\tsoftspaceq\x03K\x00U\x07buflistq\x04]q\x05U\x03posq\x06K\x00U\x03lenq\x07K\x03U\x06closedq\x08\x89U\x03bufq\tU\x03abcq\nub.')
StringIO.StringIO instance at 0xb70c122c

On 3.x I got an error:
Traceback (most recent call last):
  File stdin, line 1, in module
TypeError: _io.StringIO.__setstate__ argument should be 4-tuple, got dict

--
components: Library (Lib)
messages: 231268
nosy: alexandre.vassalotti, pitrou, serhiy.storchaka
priority: normal
severity: normal
status: open
title: StringIO.StringIO pickled in 2.7 is not unpickleable on 3.x
type: behavior
versions: Python 3.4, Python 3.5

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