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[Python-ideas] Adding`Unpicklable` to the `collections` module

Nick Coghlan ncoghlan at gmail.com
Wed Dec 1 01:57:38 CET 2010 
On Wed, Dec 1, 2010 at 8:08 AM, Masklinn <masklinn at masklinn.net> wrote:
>>  That’s why isintance+ABCs is the right test to use here.  See
>> http://docs.python.org/dev/reference/datamodel#special-method-names
> Due to Python's lookup rule, looking up most (if not all) of the special method on the instance is going to give the same result.

It's the "most" in that sentence that makes the ABC the more accurate
check of the examples given. Checking the instance does work most of
the time (since most instances don't have magic methods attached) but
fails abysmally when the instance in question is a class and the
intent is to invoke the magic methods of the metaclass (usually
'type').

Deliberately bypassing the instance with either type(x) or x.__class__
is the closest pure Python code can get to correctly following the
special method lookup rules:
http://docs.python.org/reference/datamodel.html#special-method-lookup-for-new-style-classes

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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