[Python-Dev] On breaking modules into packages Was: [issue10199] Move Demo/turtle under Lib/

[Eric Smith]

On 11/3/10 10:16 AM, Michael Foord wrote:
> On 03/11/2010 14:05, Nick Coghlan wrote:
>> On Wed, Nov 3, 2010 at 9:32 AM, Raymond Hettinger
>> <raymond.hettinger at gmail.com> wrote:
>>> Sounds like a decision to split a module into a package is a big
>>> commitment. Each of the individual file names becomes a permanent
>>> part of the API. Even future additional splits are precluded because
>>> it might break someones dotted import (i.e. not a single function can
>>> be moved between those files -- once in unittest.utils, alway in
>>> unittest.utils).
>> Can Python 2.7 pickles containing unittest classes be unpickled using
>> 2.6 or earlier? Even if nobody uses the new names for imports, I
>> believe they implicitly end up included in any pickles involving
>> affected classes (I seem to recall we've been bitten by that before
>> when moving things around).
>
> Yes, since unittest.TestCase is still available (as are all the names).
> I believe so anyway...

Actually I think the answer is "no" (assuming you could pickle a 
TestCase). Here's an example with TestLoader:

$ python27
Python 2.7.0+ (release27-maint:85878, Oct 28 2010, 06:40:25)
[GCC 4.1.2 20070626 (Red Hat 4.1.2-13)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
 >>> import unittest
 >>> x = unittest.TestLoader()
 >>> import pickle
 >>> pickle.dumps(x)
'ccopy_reg\n_reconstructor\np0\n(cunittest.loader\nTestLoader\np1\nc__builtin__\nobject\np2\nNtp3\nRp4\n.'
 >>>

$ python24
Python 2.4.4 (#1, Oct 23 2006, 13:58:00)
[GCC 4.1.1 20061011 (Red Hat 4.1.1-30)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
 >>> import pickle
 >>> 
pickle.loads('ccopy_reg\n_reconstructor\np0\n(cunittest.loader\nTestLoader\np1\nc__builtin__\nobject\np2\nNtp3\nRp4\n.')
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
   File "/usr/lib/python2.4/pickle.py", line 1394, in loads
     return Unpickler(file).load()
   File "/usr/lib/python2.4/pickle.py", line 872, in load
     dispatch[key](self)
   File "/usr/lib/python2.4/pickle.py", line 1104, in load_global
     klass = self.find_class(module, name)
   File "/usr/lib/python2.4/pickle.py", line 1138, in find_class
     __import__(module)
ImportError: No module named loader

The problem is that there is no unittest.loader in 2.4, and 
unittest.loader.TestLoader is the name that the 2.7 pickle creates. We 
see this problem every time we try and move anything in the stdlib.

-- 
Eric.