[Python-Dev] struct.pack inconsistencies between platforms

[Eli Bendersky]

On Sun, Feb 26, 2012 at 15:09, Paul Moore <p.f.moore at gmail.com> wrote:

> On 26 February 2012 12:34, Eli Bendersky <eliben at gmail.com> wrote:
> > On Sun, Feb 26, 2012 at 12:33, pmon mail <pmon.mail at gmail.com> wrote:
> >> Documentation clearly states that the 'L' is a 4 byte integer.
> >>
> >> Is this a bug? I'm I missing something?
> >>
> >
> > By default pack uses native size, not standard size. On a 64-bit machine:
>
> As the OP points out, the documentation says that the "Standard Size"
> is 4 bytes (http://docs.python.org/library/struct.html). While
> "Standard Size" doesn't appear to be defined in the documentation, and
> the start of the previous section (7.3.2.1. Byte Order, Size, and
> Alignment) clearly states that C types are represented in native
> format by default, the documentation could probably do with some
> clarification.
>
>
7.2.3.1 says, shortly after the first table:

"

Native size and alignment are determined using the C compiler’s
sizeofexpression. This is always combined with native byte order.

Standard size depends only on the format character; see the table in
the *Format
Characters* <http://docs.python.org/library/struct.html#format-characters>section.
"

To me this appears to be a reasonable definition of what "standard size"
is.

7.3.2.2 says before the size table:

"Format characters have the following meaning; the conversion between C and
Python values should be obvious given their types. The ‘Standard size’
column refers to the size of the packed value in bytes when using standard
size; that is, when the format string starts with one of '<', '>', '!' or
'='. When using native size, the size of the packed value is
platform-dependent."

Again, taken together with the previous quote, IMHO this defines the
difference between standard and native sizes clearly. If you feel
differently, feel free to open an issue suggesting a better explanation.

Eli
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