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bug#22533: Python bytecode reproducibility

From: Gábor Boskovits
Subject: bug#22533: Python bytecode reproducibility
Date: Sun, 4 Mar 2018 10:21:17 +0100

2018-03-03 23:37 GMT+01:00 Ricardo Wurmus <address@hidden>:
Hi Guix,

Marius Bakke <address@hidden> writes:

> It would be great to revive this longstanding bug!


Here’s another attempt.  As far as I understand, the timestamp in the
pyc files only affects the header.

Up until Python 3.6 (incl) the header looks like this:

  magic | timestamp | size

Since Python 3.7 the header may either contain a timestamp or a hash:

  magic | 00000000000000000000000000000000 | timestamp | size
  magic | 00000000000000000000000000000001 | hash      | size

This means we likely won’t have this problem any more with Python 3.7.
For Python 3.6 I guess we could add a final build phase that overwrites
the timestamp in the *binary*.  This needs to happen before any of the
compiled files are wrapped up in a wheel.

Should we just wait for Python 3.7 which is expected to be released in
June 2018?  We’d still have to deal with this problem in Python 2,

Is it a bad idea to override the timestamps in the generated binaries?
I think that we could avoid the recency check then, which was an
obstacle to resetting the timestamps of the source files.

GPG: BCA6 89B6 3655 3801 C3C6  2150 197A 5888 235F ACAC

Nix had this issue, it seems they have a python 3.5 solution, which
should be easy to adopt: https://github.com/NixOS/nixpkgs/issues/22570.

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