GeezerVison is showing github.com — Some tests fail when __pycache__ prefix is set · Issue #151626 · python/cpython
Some tests fail when __pycache__ prefix is set #151626DescriptionBug report
Bug description:
Some tests that check .pyc files creation are failing when sys.pycache_prefix is set.
List of tests that failed on Arm64 MacOS (maybe there's more in skipped ones):
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test.test_inspect.test_inspect.TestModuleCLI.test_details_option_with_package
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test.test_import.PycacheTests.test_import_pyc_path
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test.test_import.PycacheTests.test_unwritable_directory
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test.test_importlib.test_util.PEP3147Tests.test_cache_from_source
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test.test_importlib.test_util.PEP3147Tests.test_cache_from_source_cwd
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test.test_importlib.test_util.PEP3147Tests.test_cache_from_source_no_dot
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test.test_importlib.test_util.PEP3147Tests.test_cache_from_source_optimization_None
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test.test_importlib.test_util.PEP3147Tests.test_cache_from_source_optimization_empty_string
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test.test_importlib.test_util.PEP3147Tests.test_cache_from_source_optimization_set
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test.test_importlib.test_util.PEP3147Tests.test_cache_from_source_path_like_arg
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test.test_py_compile.PyCompileCLITestCase.test_with_files
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test.test_py_compile.PyCompileTestsBase.test_double_dot_no_clobber
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test.test_compileall.CompileallTestsBase.test_include_on_stdin
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test.test_compileall.CompileallTestsBase.test_multiple_runs
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test.test_compileall.CompileallTestsBase.test_symlink_loop
example: PYTHONPYCACHEPREFIX="$HOME/__pycache__" ./python.exe -m test test.test_compileall test.test_import test.test_importlib.test_util test.test_inspect.test_inspect test.test_py_compile -v
output (edited for clarity and length): testres.txt
CPython versions tested on:
CPython main branch
Operating systems tested on:
macOS
Linked PRs
Activitychanged the title [-]Some tests fail when \_\_pycache\_\_ prefix is set[/-] [+]Some tests fail when __pycache__ prefix is set[/+] on Jun 18, 2026zangjiucheng commented on Jun 22, 2026 Hey there, thanks for the detailed report and the reproduction command. Verified locally on macOS ARM64 (Python 3.16.0a0) with PYTHONPYCACHEPREFIX set to a temp directory.
The fix neutralizes sys.pycache_prefix (and strips PYTHONPYCACHEPREFIX from subprocess environments) in all five test files. Verified locally on macOS ARM64 with PYTHONPYCACHEPREFIX set; all the tests you listed now pass, including the three test_inspect.TestModuleCLI cases and the full PEP3147Tests suite.
I will resolve and attach the PR asap. gpshead commented on Jul 1, 2026
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