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To: python-list@python.org
From: Mark Lawrence <breamoreboy@yahoo.co.uk>
Subject: Python 3.3 can't sort memoryviews as they're unorderable
Date: Sun, 21 Oct 2012 12:24:32 +0100
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Xref: csiph.com comp.lang.python:31846

http://docs.python.org/dev/whatsnew/3.3.html states "memoryview 
comparisons now use the logical structure of the operands and compare 
all array elements by value".  So I'd have thought that you should be 
able to compare them and hence sort them, but this is the state of play.

Python 3.3.0 (v3.3.0:bd8afb90ebf2, Sep 29 2012, 10:55:48) [MSC v.1600 32 
bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
 >>> memoryview(bytearray(range(5))) == memoryview(bytearray(range(5)))
True
 >>> memoryview(bytearray(range(5))) != memoryview(bytearray(range(5)))
False
 >>> memoryview(bytearray(range(5))) < memoryview(bytearray(range(5)))
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
TypeError: unorderable types: memoryview() < memoryview()

Okay then, let's subclass memoryview to provide the functionality.

 >>> class Test(memoryview):
...     pass
...
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
TypeError: type 'memoryview' is not an acceptable base type

Oh dear. 
http://docs.python.org/py3k/library/stdtypes.html#typememoryview only 
gives examples of equality comparisons and there was nothing that I 
could see in PEP3118 to explain the rationale behind the lack of other 
comparisons.  What have I missed?

-- 
Cheers.

Mark Lawrence.