Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Chris Angelico <rosuav@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Pyhon 2.x or 3.x, which is faster?
Date: Wed, 9 Mar 2016 11:38:13 +1100
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On Wed, Mar 9, 2016 at 11:34 AM, Michael Torrie <torriem@gmail.com> wrote:
> On 03/07/2016 05:45 PM, Chris Angelico wrote:
>> On Tue, Mar 8, 2016 at 11:22 AM, BartC <bc@freeuk.com> wrote:
>>>
>>> (Is a byte string the same as a byte array? Is a byte array the same as an
>>> array.array? If I remove this line from my code, where 'data' has just been
>>> read from a file:
>>>
>>>    data=array.array('B',data)
>>>
>>> then it still works - Python 3. But not on Python 2. If I do .read on a
>>> binary file I get a byte string in Python 3, but a string in Python 2. That
>>> sort of mess.
>>
>> The default string in Py2 *is* a byte string.
>
> There are some interesting differences I found between a Python 2 string
> (composed of bytes) and a Python 3 byte string, such as what you'd get
> from calling read() on a file handle opened in binary mode.  That is in
> Python 2, indexing a string returns a string of length 1.  In Python
> 3.5, indexing a byte string returns a value, the equivalent of calling
> ord() on the single byte string.  This makes it a bit difficult to make
> the code easily work between Python 2 and 3 and handle bytes.  Any ideas
> there?

As Steven commented, this is probably a design flaw in the Py3 bytes
type, but it can't be changed now. For perfect compatibility, just
slice:

>>> b"asdf"[2:3] # Py2
'd'
>>> b"asdf"[2:3] # Py3
b'd'

Works in both versions, with the only difference being the repr.

It's a bit clunky, but it does work.

ChrisA