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

[Paul Moore]

On 24 February 2015 at 20:32, Barry Warsaw <barry at python.org> wrote:
>>To modify an archive could be done using
>>
>>    python -m zipapp old.pyz new.pyz [-p interpreter]
>>
>>Default is to strip the shebang (no -p option). There's no option to
>>omit the target and do an inplace update because I feel the default
>>action (strip the shebang from the existing file with no backup) is
>>too dangerous.
>
> You have to be careful about the case where old.pyz == new.pyz (e.g. either
> handling this case safely or complaining loudly) , but also you could handle
> it by using a .tmp file and renaming.  E.g. old.pyz -> old.pyz.bak and
> old.pyz.tmp -> old.pyz.

There are a *lot* of obscure failure modes here. What if old and new
are symlinks (or hard links) to the same file? What if a .tmp file
already exists? What if the user hits Ctrl-C at a bad moment?

On the principle of keeping it simple, I prefer just requiring a
target, giving an error if the source name and target name are the
same (which still leaves loopholes for the determined fool on case
insensitive filesystems :-)) and just documenting that inplace
modification isn't supported. The PEP clearly states that it's
*minimal* tooling, after all...

>
>>3. What to call the "show the shebang line" option
>
> I don't know how useful this is, given that (on *nix at least) you can
> effectively do the same with head(1).

I don't think it's that useful, TBH (although will head not print
binary junk if there is no shebang line?) I quite like Brett's
suggestion of --info, and maybe be a bit verbose:

$ python -m zipapp foo.pyz --info
Interpreter: /usr/bin/python
$ python -m zipapp bar.pyz --info
Interpreter: <none>

I can't see it being useful for scripting, and if it matters, there's
always get_interpreter() then. It's mainly just as a diagnostic for
people who are getting the wrong interpreter invoked.

Paul