Hi,
gzip.NO_TIMESTAMP sounds like a good idea. But I'm not sure about
changing the default behavior. I would prefer to leave it unchanged.
I guess that your problem is that you don't access gzip directly, but
uses a higher level API which doesn't give access to the timestamp
parameter, like the tarfile module?
If your usecase is reproducible build, you may follow py_compile
behavior: the default behavior depends if the SOURCE_DATE_EPOCH
environment variable is set or not:
def _get_default_invalidation_mode():
if os.environ.get('SOURCE_DATE_EPOCH'):
return PycInvalidationMode.CHECKED_HASH
else:
return PycInvalidationMode.TIMESTAMP
Victor
On Wed, Apr 14, 2021 at 6:34 PM Joachim Wuttke <[email protected]> wrote:
>
> gzip compression, using class GzipFile from gzip.py, by default
> inserts a timestamp to the compressed stream. If the optional
> argument `mtime` is absent or None, then the current time is used [1].
>
> This makes outputs non-deterministic, which can badly confuse
> unsuspecting users: If you run "diff" over two outputs to see
> whether they are unaffected by changes in your application,
> then you would not expect that the *.gz binaries differ just
> because they were created at different times.
>
> I'd propose to introduce a new constant `NO_TIMESTAMP` as
> possible value of `mtime`.
>
> Furthermore, if policy about API changes allows, I'd suggest
> that `NO_TIMESTAMP` become the new default value for `mtime`.
>
> How to proceed from here? Is this the kind of proposals that
> has to go through a PEP?
>
> - Joachim
>
> [1]
> https://github.com/python/cpython/blob/6f1e8ccffa5b1272a36a35405d3c4e4bbba0c082/Lib/gzip.py#L163
>
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