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Steve Holden | 6 Oct 08:41
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[Fwd: In Python 2.6, bytes is str]

This does make it look rather as though bytes == str was a decision
whose consequences weren't fully appreciated before implementation.

Was this horror anticipated?

regards
 Steve

-------- Original Message --------
Subject: In Python 2.6, bytes is str
Date: Sun, 05 Oct 2008 22:30:17 -0700
From: Bryan Olson <fakeaddress <at> nowhere.org>
Organization: at&t http://my.att.net/
To: python-list <at> python.org
Newsgroups: gmane.comp.python.general

Python 3 has the 'bytes' type, which the string type I've long wanted in
various languages. Among other advantages, it is immutable, and
therefore bytes objects can be dict keys. There's a mutable version too,
called "bytearray".

In Python 2.6, the name 'bytes' is defined, and bound to str. The 2.6
assignment presents some pitfalls. Be aware.

Consider constructing a bytes object as:

    b = bytes([68, 255, 0])

In Python 3.x, len(b) will be 3, which feels right.
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Brett Cannon | 6 Oct 08:55
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Re: [Fwd: In Python 2.6, bytes is str]

On Sun, Oct 5, 2008 at 11:43 PM, Steve Holden <steve <at> holdenweb.com> wrote:
> This does make it look rather as though bytes == str was a decision
> whose consequences weren't fully appreciated before implementation.
>

Well, you could say that about almost any change.

> Was this horror anticipated?

I didn't anticipate it.

>
> regards
>  Steve
>
> -------- Original Message --------
> Subject: In Python 2.6, bytes is str
> Date: Sun, 05 Oct 2008 22:30:17 -0700
> From: Bryan Olson <fakeaddress <at> nowhere.org>
> Organization: at&t http://my.att.net/
> To: python-list <at> python.org
> Newsgroups: gmane.comp.python.general
>
>
> Python 3 has the 'bytes' type, which the string type I've long wanted in
> various languages. Among other advantages, it is immutable, and
> therefore bytes objects can be dict keys. There's a mutable version too,
> called "bytearray".
>
> In Python 2.6, the name 'bytes' is defined, and bound to str. The 2.6
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Nick Coghlan | 6 Oct 13:17

Re: [Fwd: In Python 2.6, bytes is str]

Brett Cannon wrote:
> What I would like to know if there are any other gotchas beyond the
> constructor as all of the other uses act as you would expect.

Mainly that indexing returns one character substrings instead of ints.

The bytes type is there as an indicator of what bytes literals represent
in 2.6 - yes, that's not the same thing as what they represent in 3.0,
and no, you don't magically get the benefits of byte/str separation in
the 2.x series.

Maybe that could be caveat'ed better somewhere in the docs, but it does
reflect the reality of the situation.

Cheers,
Nick.

--

-- 
Nick Coghlan   |   ncoghlan <at> gmail.com   |   Brisbane, Australia
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            http://www.boredomandlaziness.org
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Guido van Rossum | 7 Oct 22:13
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Re: [Fwd: In Python 2.6, bytes is str]

On Sun, Oct 5, 2008 at 11:43 PM, Steve Holden <steve <at> holdenweb.com> wrote:
> This does make it look rather as though bytes == str was a decision
> whose consequences weren't fully appreciated before implementation.
>
> Was this horror anticipated?

It was well understood that the bytes "type" in 2.6 and the bytes type
in 3.0 would behave quite different. Attempts to come up with a
separate bytes type that behaved more like its 3.0 counterpart were
doomed, because there just are too many places where the usage was
ambiguous. We should probably have written a PEP about this just to
prevent the discussion from being repeated all over again in this
thread.

The only two anticipated *reasonable* uses in 2.6 were the bytes
literal (b'abc') and tests for isinstance(x, bytes), which are flags
for 2to3 to keep these usages as bytes, not str.

I have no intention of rolling this back. It isn't compatible with
3.0, but then, 2.6 and 3.0 aren't in general meant to be compatible --
2.6 is a stepping stone, but that's not the same thing. It is
backwards compatible with prior versions because it is new in 2.6, so
it shouldn't break old code. I have only limited sympathy for people
who don't read documentation in this case.

--Guido

> -------- Original Message --------
> Subject: In Python 2.6, bytes is str
> Date: Sun, 05 Oct 2008 22:30:17 -0700
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Christian Heimes | 8 Oct 01:25
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Re: [Fwd: In Python 2.6, bytes is str]

Guido van Rossum wrote:
> It was well understood that the bytes "type" in 2.6 and the bytes type
> in 3.0 would behave quite different. Attempts to come up with a
> separate bytes type that behaved more like its 3.0 counterpart were
> doomed, because there just are too many places where the usage was
> ambiguous. We should probably have written a PEP about this just to
> prevent the discussion from being repeated all over again in this
> thread.
> 
> The only two anticipated *reasonable* uses in 2.6 were the bytes
> literal (b'abc') and tests for isinstance(x, bytes), which are flags
> for 2to3 to keep these usages as bytes, not str.

Full ack!

I replies this to the op on the general Python list:
---
I guess you got the intention of the bytes alias wrong. It's partly my 
fault because I didn't document the bytes alias. We are well aware that 
the bytes alias in 2.6 isn't fully compatible with the bytes type in 
3.0. The bytes alias isn't MEANT to be compatible, too.  :)

At first I wanted to backport the bytes type from 3.0 to 2.6. But it was 
too many work and the implications of yet another types were too 
complex. So I just added the alias in order to help people with writing 
forward compatible code like e.g. isinstance(egg, bytes).

Summa summarum the bytes alias was added for documentary purpose and to 
aid the 2to3 transition of code where 'str' is ambiguous.
--
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Steve Holden | 8 Oct 02:37
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Re: [Fwd: In Python 2.6, bytes is str]

Christian Heimes wrote:
> Guido van Rossum wrote:
[...]
>> I have no intention of rolling this back. It isn't compatible with
>> 3.0, but then, 2.6 and 3.0 aren't in general meant to be compatible --
>> 2.6 is a stepping stone, but that's not the same thing. It is
>> backwards compatible with prior versions because it is new in 2.6, so
>> it shouldn't break old code. I have only limited sympathy for people
>> who don't read documentation in this case.
> 
> Maybe the documentation isn't clear enough what purpose the bytes alias
> serves? I spent 5 minutes with the docs but I wasn't able to find a good
> explanation of the bytes alias
> 
Yes, I think all that's really needed is a clarification in the
documentation. Just so people expect slightly kooky behavior of the kind
originally noted.

regards
 Steve
--

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Steve Holden        +1 571 484 6266   +1 800 494 3119
Holden Web LLC              http://www.holdenweb.com/

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