… and that leads to these test failures:

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix build python@3 --rounds=2 -K

[...]

======================================================================
FAIL: test_bad_marshal (test.test_importlib.source.test_file_loader.Source_SourceLoaderBadBytecodeTestPEP302)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/util.py", line 22, in wrapper
    to_return = fxn(*args, **kwargs)
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 452, in test_bad_marshal
    self._test_bad_marshal()
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 342, in _test_bad_marshal
    self.import_(file_path, '_temp')
AssertionError: EOFError not raised

======================================================================
FAIL: test_no_marshal (test.test_importlib.source.test_file_loader.Source_SourceLoaderBadBytecodeTestPEP302)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/util.py", line 22, in wrapper
    to_return = fxn(*args, **kwargs)
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 441, in test_no_marshal
    self._test_no_marshal()
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 322, in _test_no_marshal
    self.import_(file_path, '_temp')
AssertionError: EOFError not raised

======================================================================
FAIL: test_non_code_marshal (test.test_importlib.source.test_file_loader.Source_SourceLoaderBadBytecodeTestPEP302)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/util.py", line 22, in wrapper
    to_return = fxn(*args, **kwargs)
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 445, in test_non_code_marshal
    self._test_non_code_marshal()
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 331, in _test_non_code_marshal
    self.import_(file_path, '_temp')
AssertionError: ImportError not raised

======================================================================
FAIL: test_old_timestamp (test.test_importlib.source.test_file_loader.Source_SourceLoaderBadBytecodeTestPEP302)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/util.py", line 22, in wrapper
    to_return = fxn(*args, **kwargs)
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 471, in test_old_timestamp
    self.assertEqual(bytecode_file.read(4), source_timestamp)
AssertionError: b'\x01\x00\x00\x00' != b'\x7f\xc7\x04W'

======================================================================
FAIL: test_bad_marshal (test.test_importlib.source.test_file_loader.Source_SourceLoaderBadBytecodeTestPEP451)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/util.py", line 22, in wrapper
    to_return = fxn(*args, **kwargs)
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 452, in test_bad_marshal
    self._test_bad_marshal()
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 342, in _test_bad_marshal
    self.import_(file_path, '_temp')
AssertionError: EOFError not raised

======================================================================
FAIL: test_no_marshal (test.test_importlib.source.test_file_loader.Source_SourceLoaderBadBytecodeTestPEP451)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/util.py", line 22, in wrapper
    to_return = fxn(*args, **kwargs)
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 441, in test_no_marshal
    self._test_no_marshal()
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 322, in _test_no_marshal
    self.import_(file_path, '_temp')
AssertionError: EOFError not raised

======================================================================
FAIL: test_non_code_marshal (test.test_importlib.source.test_file_loader.Source_SourceLoaderBadBytecodeTestPEP451)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/util.py", line 22, in wrapper
    to_return = fxn(*args, **kwargs)
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 445, in test_non_code_marshal
    self._test_non_code_marshal()
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 331, in _test_non_code_marshal
    self.import_(file_path, '_temp')
AssertionError: ImportError not raised

======================================================================
FAIL: test_old_timestamp (test.test_importlib.source.test_file_loader.Source_SourceLoaderBadBytecodeTestPEP451)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/util.py", line 22, in wrapper
    to_return = fxn(*args, **kwargs)
  File "/tmp/guix-build-python-minimal-3.4.3.drv-0/Python-3.4.3/Lib/test/test_importlib/source/test_file_loader.py", line 471, in test_old_timestamp
    self.assertEqual(bytecode_file.read(4), source_timestamp)
AssertionError: b'\x01\x00\x00\x00' != b'\x7f\xc7\x04W'

----------------------------------------------------------------------
Ran 951 tests in 1.102s

FAILED (failures=8, skipped=19, expected failures=1)
Makefile:958: recipe for target 'test' failed
--8<---------------cut here---------------end--------------->8---

‘test_old_timestamp’ clearly needs to be adjusted to account for the
change.  The others have to do with the bytecode loader, so it’s
probably a similar story.  Could you look into it?

Perhaps you tested with SOURCE_DATE_EPOCH unset?

Thanks for working on this, it’s an important bug to fix!

Ludo’.