[Python-Dev] Request for Pronouncement: PEP 441 - Improving Python ZIP Application Support

[Thomas Wouters]

On Mon, Feb 23, 2015 at 8:24 PM, Paul Moore <p.f.moore at gmail.com> wrote:

> On 23 February 2015 at 19:01, Daniel Holth <dholth at gmail.com> wrote:
> > Sounds reasonable. It could be done by just reading the entire file
> > contents after the shebang and re-writing them with the necessary
> > offset all in RAM, truncating the file if necessary, without involving
> > the zipfile module very much; the shebang could have some amount of
> > padding by default; the file could just be re-compressed in memory
> > depending on your appetite for complexity.
>
> The biggest problem with that is finding the end of the prefix data.
> Frankly it's easier just to write a new prefix then use the zipfile
> module to rewrite all of the content. That's what the current code
> does writing to a new file.


I don't think you need to rewrite all of the contents, if you don't mind
poking into zipfile internals:

endrec = zipfile._EndRecData(f)
prefix_length = endrec[zipfile._ECD_LOCATION] - endrec[zipfile._ECD_SIZE] -
endrec[zipfile._ECD_OFFSET]

I do something similar to get at the prefix, although I need the zipfile
opened anyway, so I use:

endrec = zipfile._EndRecData(f) # pylint: disable=protected-access
zf = zipfile.ZipFile(f)
# endrec is None if reading it failed, but then ZipFile should have
# raised an exception...
assert endrec
prefix_len = zf.start_dir - endrec[zipfile._ECD_OFFSET]  # pylint:
disable=protected-access


Paul
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Thomas Wouters <thomas at python.org>

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