GNU bug report logs - #22533
Non-determinism in python-3 ".pyc" bytecode

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From: Ricardo Wurmus <rekado <at> elephly.net>
To: Gábor Boskovits <boskovits <at> gmail.com>
Cc: Marius Bakke <mbakke <at> fastmail.com>, 22533 <at> debbugs.gnu.org
Subject: bug#22533: Python bytecode reproducibility
Date: Mon, 05 Mar 2018 01:05:04 +0100

Ricardo Wurmus <rekado <at> elephly.net> writes:

> Unfortunately, this doesn’t fix all reproducibility problems with numpy:
>
> --8<---------------cut here---------------start------------->8---
> Binary files /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0-check/lib/python3.6/site-packages/numpy/distutils/__pycache__/__config__.cpython-36.pyc and /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0/lib/python3.6/site-packages/numpy/distutils/__pycache__/__config__.cpython-36.pyc differ
> Binary files /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0-check/lib/python3.6/site-packages/numpy/distutils/__pycache__/exec_command.cpython-36.pyc and /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0/lib/python3.6/site-packages/numpy/distutils/__pycache__/exec_command.cpython-36.pyc differ
> Binary files /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0-check/lib/python3.6/site-packages/numpy/distutils/__pycache__/system_info.cpython-36.pyc and /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0/lib/python3.6/site-packages/numpy/distutils/__pycache__/system_info.cpython-36.pyc differ
> Binary files /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0-check/lib/python3.6/site-packages/numpy/__pycache__/__config__.cpython-36.pyc and /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0/lib/python3.6/site-packages/numpy/__pycache__/__config__.cpython-36.pyc differ
> Binary files /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0-check/lib/python3.6/site-packages/numpy/__pycache__/version.cpython-36.pyc and /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0/lib/python3.6/site-packages/numpy/__pycache__/version.cpython-36.pyc differ
> Binary files /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0-check/lib/python3.6/site-packages/numpy/testing/nose_tools/__pycache__/utils.cpython-36.pyc and /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0/lib/python3.6/site-packages/numpy/testing/nose_tools/__pycache__/utils.cpython-36.pyc differ
> --8<---------------cut here---------------end--------------->8---

Here’s what diffoscope says:

--8<---------------cut here---------------start------------->8---
diffoscope /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0{-check,}/lib/python3.6/site-packages/numpy/__pycache__/version.cpython-36.pyc
--- /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0-check/lib/python3.6/site-packages/numpy/__pycache__/version.cpython-36.pyc
+++ /gnu/store/kd06ql8fynlydymzhhnwk2lh0778dwcc-python-numpy-1.14.0/lib/python3.6/site-packages/numpy/__pycache__/version.cpython-36.pyc
@@ -1,8 +1,8 @@
-00000000: 330d 0d0a fa87 9c5a 2601 0000 e300 0000  3......Z&.......
+00000000: 330d 0d0a c485 9c5a 2601 0000 e300 0000  3......Z&.......
 00000010: 0000 0000 0000 0000 0001 0000 0040 0000  .............@..
 00000020: 0073 2000 0000 6400 5a00 6400 5a01 6400  .s ...d.Z.d.Z.d.
 00000030: 5a02 6401 5a03 6402 5a04 6504 731c 6502  Z.d.Z.d.Z.e.s.e.
 00000040: 5a01 6403 5300 2904 7a06 312e 3134 2e30  Z.d.S.).z.1.14.0
 00000050: da28 3639 3134 6262 3431 6630 6662 3363  .(6914bb41f0fb3c
 00000060: 3162 6135 3030 6261 6534 6537 6436 3731  1ba500bae4e7d671
 00000070: 6461 3935 3336 3738 3666 544e 2905 da0d  da9536786fTN)...
--8<---------------cut here---------------end--------------->8---

In other words: this is the timestamp field of the pyc file.

Maybe this can be avoided by setting DETERMINISTIC_BUILD in the
python-build-system?

--
Ricardo

GPG: BCA6 89B6 3655 3801 C3C6  2150 197A 5888 235F ACAC
https://elephly.net

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