[Python-Dev] Why does _pyio.*.readinto have to work with 'b' arrays? (original) (raw)

Nikolaus Rath Nikolaus at rath.org
Sun Jun 15 06:57:12 CEST 2014

On 06/14/2014 09:31 PM, Nick Coghlan wrote:

On 15 June 2014 10:41, Benjamin Peterson <benjamin at python.org> wrote:

On Sat, Jun 14, 2014, at 15:39, Nikolaus Rath wrote:

It seems to me that a much cleaner solution would be to simply declare pyio's readinto to only work with bytearrays, and to explicitly raise a (more helpful) TypeError if anything else is passed in.

That seems reasonable. I don't think pyio's behavior is terribly important compared to the C io module. pyio was written before the various memoryview fixes that were implemented in Python 3.3 - it seems to me it would make more sense to use memoryview to correctly handle arbitrary buffer exporters (we implemented similar fixes for the base64 module in 3.4).

Definitely. But is there a way to do that without writing C code?

My attempts failed:

from array import array a = array('b', b'x'*10) am = memoryview(a) am[:3] = b'foo' Traceback (most recent call last): File "", line 1, in ValueError: memoryview assignment: lvalue and rvalue have different structures am[:3] = memoryview(b'foo') Traceback (most recent call last): File "", line 1, in ValueError: memoryview assignment: lvalue and rvalue have different structures am.format = 'B' Traceback (most recent call last): File "", line 1, in AttributeError: attribute 'format' of 'memoryview' objects is not writable

The only thing that works is:

am[:3] = array('b', b'foo')

but that's again specific to a being a 'b'-array.

Best, -Nikolaus

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