[Python-porting] Pickling unbound methods on Python 3

[M.-A. Lemburg]

cool-RR wrote:
> On Sat, May 29, 2010 at 5:46 PM, R. David Murray <rdmurray at bitdance.com>wrote:
> 
>> On Fri, 28 May 2010 21:55:28 +0200, cool-RR wrote:
>>> One person told me that given an unbound method in Python 3.x, it's
>>> *impossible* to tell to which class it belongs. Is it true?
>>
>> I believe that that is true.  In Python3 there is no such thing as an
>> unbound method as a distinct object type.  There are functions, and
>> there are bound methods.  See the second sentence in this section:
>>
>>
>> http://docs.python.org/release/3.0.1/whatsnew/3.0.html#operators-and-special-methods
> 
> 
> I see. Where would be a good place to discuss this decision? I would want
> 3.2 to allow pickling of unbound methods.

Unbound methods don't exist in Python3. You only have functions and
(bound) methods.

You can see that if you try to call an unbound method with a
non-instance first arg:

>>> class X:
...  def test(self): return 42
...
>>> X.test(X())
42
>>> X.test(3)
42

Doing the same in Python2 gives an error:

>>> X.test(X())
42
>>> X.test(3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unbound method test() must be called with X instance as first argument (got int instance
instead)

-- 
Marc-Andre Lemburg
eGenix.com

Professional Python Services directly from the Source  (#1, May 29 2010)
>>> Python/Zope Consulting and Support ...        http://www.egenix.com/
>>> mxODBC.Zope.Database.Adapter ...             http://zope.egenix.com/
>>> mxODBC, mxDateTime, mxTextTools ...        http://python.egenix.com/
________________________________________________________________________
2010-07-19: EuroPython 2010, Birmingham, UK                50 days to go

::: Try our new mxODBC.Connect Python Database Interface for free ! ::::


   eGenix.com Software, Skills and Services GmbH  Pastor-Loeh-Str.48
    D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg
           Registered at Amtsgericht Duesseldorf: HRB 46611
               http://www.egenix.com/company/contact/