[Python-Dev] Fwd: Python 3.3 can't sort memoryviews as they're unorderable (original) (raw)

Mark Lawrence breamoreboy at yahoo.co.uk
Tue Oct 23 02:04:47 CEST 2012

-------- Original Message -------- Subject: Python 3.3 can't sort memoryviews as they're unorderable Date: Sun, 21 Oct 2012 12:24:32 +0100 From: Mark Lawrence <breamoreboy at yahoo.co.uk> To: python-list at python.org Newsgroups: gmane.comp.python.general

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 "", line 1, in 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 "", line 1, in 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?

Nobody on the main Python ml could answer this so can someone please explain the background to how memoryviews work in this instance as I'm confused, thanks.

Mark Lawrence.

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