Python 3.1.2 and marshal

[raj]

On Jul 17, 10:11 pm, Thomas Jollans <tho... at jollans.com> wrote:
[Snip]
> So, the contents of the file is identical, but Python 3 reads the whole
> file, Python 2 reads only the data it uses.
>
> This looks like a simple optimisation: read the whole file at once,
> instead of byte-by-byte, to improve performance when reading large
> objects. (such as Python modules...)
>

Good analysis and a nice catch.  Thanks. It is likely that the intent
is to optimize performance.

> The question is: was storing multiple objects in sequence an intended
> use of the marshal module?

The documentation (http://docs.python.org/py3k/library/marshal.html)
for marshal itself states (emphasis added by me),

marshal.load(file)¶

    Read *one value* from the open file and return it. If no valid
value is read (e.g. because the data has a different Python version’s
incompatible marshal format), raise EOFError, ValueError or TypeError.
The file must be an open file object opened in binary mode ('rb' or 'r
+b').

This suggests that support for reading multiple values is intended.

> I doubt it. You can always wrap your data in
> tuples or use pickle.
>

The code that I am moving to 3.x dates back to the python 1.5 days,
when marshal was significantly faster than pickle and Zope was
evolutionarily at the Bobo stage :-). I have switched the current code
to pickle - makes more sense.  The pickle files are a bit larger and
loading it is a tad bit slower, but nothing that makes even a
noticeable difference for my use case. Thanks.

raj