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[2.7] bpo-29514: Check magic number for bugfix releases #2160

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ncoghlan merged 1 commit into from
Jun 13, 2017
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[2.7] bpo-29514: Check magic number for bugfix releases #2160

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[2.7] bpo-29514: Check magic number for bugfix releases 
Add a test to check the current MAGIC_NUMBER against the
expected number for the release if the current release is
at candidate or final level. On test failure, describe to
the developer the procedure for changing the magic number.

This ensures that pre-merge CI will automatically pick up
on magic number changes in maintenance releases (and
explain why those are problematic), rather than relying on
all core developers to be aware of the implications of
such changes.
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@appeltel @ncoghlan
appeltel authored and ncoghlan committed Jun 13, 2017
commit 4fe9a65e470572078a2a2a10dee7e6a337c1e391
58 changes: 58 additions & 0 deletions Lib/test/test_import_magic.py
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import imp
import sys

import unittest

# Note:
# In Python 3.x, this test case is in Lib/test/test_importlib/test_util.py

class MagicNumberTests(unittest.TestCase):
"""
Test release compatibility issues relating to precompiled bytecode
"""
@unittest.skipUnless(
sys.version_info.releaselevel in ('final', 'release'),
'only applies to candidate or final python release levels'
)
def test_magic_number(self):
"""
Each python minor release should generally have a MAGIC_NUMBER
that does not change once the release reaches candidate status.

Once a release reaches candidate status, the value of the constant
EXPECTED_MAGIC_NUMBER in this test should be changed.
This test will then check that the actual MAGIC_NUMBER matches
the expected value for the release.

In exceptional cases, it may be required to change the MAGIC_NUMBER
for a maintenance release. In this case the change should be
discussed in python-dev. If a change is required, community
stakeholders such as OS package maintainers must be notified
in advance. Such exceptional releases will then require an
adjustment to this test case.
"""
EXPECTED_MAGIC_NUMBER = 62211
raw_magic = imp.get_magic()
actual = (ord(raw_magic[1]) << 8) + ord(raw_magic[0])

msg = (
"To avoid breaking backwards compatibility with cached bytecode "
"files that can't be automatically regenerated by the current "
"user, candidate and final releases require the current "
"importlib.util.MAGIC_NUMBER to match the expected "
"magic number in this test. Set the expected "
"magic number in this test to the current MAGIC_NUMBER to "
"continue with the release.\n\n"
"Changing the MAGIC_NUMBER for a maintenance release "
"requires discussion in python-dev and notification of "
"community stakeholders."
)
self.assertEqual(EXPECTED_MAGIC_NUMBER, actual)#, msg)


def test_main():
from test.support import run_unittest
run_unittest(MagicNumberTests)

if __name__ == '__main__':
test_main()