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bpo-38735: Don't fail when importing from / with sys.pycache_prefix set #30456

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Merged
merged 6 commits into from
Aug 18, 2025
Merged

bpo-38735: Don't fail when importing from / with sys.pycache_prefix set #30456

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570fb35
bpo-38735: Don't crash when importing from / with pycache_prefix set
encukou Jan 7, 2022
7e4b5e5
Add a blurb
encukou Jan 7, 2022
40731a2
Merge branch 'main' into cacheprefix-slash
serhiy-storchaka Feb 24, 2024
9f464e8
Merge in the main branch
encukou Aug 2, 2025
7a277ec
Use slicing
encukou Aug 4, 2025
d2d17a0
Add test
encukou Aug 4, 2025
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3 changes: 2 additions & 1 deletion Lib/importlib/_bootstrap_external.py
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Original file line number Diff line number Diff line change
Expand Up @@ -297,7 +297,8 @@ def cache_from_source(path, debug_override=None, *, optimization=None):
# Strip initial drive from a Windows path. We know we have an absolute
# path here, so the second part of the check rules out a POSIX path that
# happens to contain a colon at the second character.
if head[1] == ':' and head[0] not in path_separators:
# Slicing avoids issues with an empty (or short) `head`.
if head[1:2] == ':' and head[0:1] not in path_separators:
head = head[2:]

# Strip initial path separator from `head` to complete the conversion
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12 changes: 12 additions & 0 deletions Lib/test/test_importlib/test_util.py
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Expand Up @@ -580,6 +580,18 @@ def test_cache_from_source_respects_pycache_prefix_relative(self):
self.util.cache_from_source(path, optimization=''),
os.path.normpath(expect))

@unittest.skipIf(sys.implementation.cache_tag is None,
'requires sys.implementation.cache_tag to not be None')
def test_cache_from_source_in_root_with_pycache_prefix(self):
# Regression test for gh-82916
pycache_prefix = os.path.join(os.path.sep, 'tmp', 'bytecode')
path = 'qux.py'
expect = os.path.join(os.path.sep, 'tmp', 'bytecode',
f'qux.{self.tag}.pyc')
with util.temporary_pycache_prefix(pycache_prefix):
with os_helper.change_cwd('/'):
self.assertEqual(self.util.cache_from_source(path), expect)

@unittest.skipIf(sys.implementation.cache_tag is None,
'requires sys.implementation.cache_tag to not be None')
def test_source_from_cache_inside_pycache_prefix(self):
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2022-01-07-16-56-57.bpo-38735.NFfJX6.rst
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@@ -0,0 +1,2 @@
Fix failure when importing a module from the root directory on unix-like
platforms with sys.pycache_prefix set.
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