[Python-Dev] PEP 450 adding statistics module (original) (raw)

Oscar Benjamin oscar.j.benjamin at gmail.com
Mon Sep 9 14:57:50 CEST 2013

On 9 September 2013 12:56, Nick Coghlan <ncoghlan at gmail.com> wrote:

Alternatively, I thought there was discussion a long time ago about getting numpy's (or even further back, numeric's?) array type into the core. Python has an array type which I don't think gets a lot of use (or love). Might it be worthwhile to make sure the PEP 450 package works with that? Then extend it to multiple dimensions? Or just bite the bullet and get numpy's array type into the Python core once and for all?

Sort of Tulip for arrays... Aka memoryview :) Stefan Krah already fixed most of the multidimensional support issues in 3.3 (including the "cast" method to reinterpret the contents in a different format). The main missing API elements are multidimensional slicing and the ability to export them from types defined in Python.

Being very familiar with numpy's ndarrays and not so much with memoryviews this prompted me to go and have a look at them.

How exactly are you supposed to create a multidimensional array using memoryviews? The best I could come up with was something like:

$ py -3.3 Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information.

import array v = memoryview(array.array('b', [1, 2, 3, 4])).cast('b', (2, 2)) v.shape (2, 2)

However I don't seem to be able to access the elements:

v[0, 1] Traceback (most recent call last): File "", line 1, in TypeError: memoryview: invalid slice key v[0] Traceback (most recent call last): File "", line 1, in NotImplementedError: multi-dimensional sub-views are not implemented v[0:1] <memory at 0x00DF8B70> v[0:1].shape (1, 2) v[0:1][0] Traceback (most recent call last): File "", line 1, in NotImplementedError: multi-dimensional sub-views are not implemented v[1] Traceback (most recent call last): File "", line 1, in NotImplementedError: multi-dimensional sub-views are not implemented v[:, 1] Traceback (most recent call last): File "", line 1, in TypeError: memoryview: invalid slice key v[1, :] Traceback (most recent call last): File "", line 1, in TypeError: memoryview: invalid slice key

And the .cast method bails if you try to use a more useful type code:

v = memoryview(array.array('q', [1, 2, 3, 4])).cast('q', (2, 2)) Traceback (most recent call last): File "", line 1, in TypeError: memoryview: cannot cast between two non-byte formats

Oscar

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