Set sys.flags.debug to 0 by default by hippi345 · Pull Request #1219 · oracle/graalpython · GitHub
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Set sys.flags.debug to 0 by default - #1219

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hippi345:fix/1213-sys-flags-debug
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Set sys.flags.debug to 0 by default#1219
hippi345 wants to merge 1 commit into
oracle:masterfrom
hippi345:fix/1213-sys-flags-debug

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@hippi345

@hippi345 hippi345 commented Oct 17, 2026 •
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Summary

CPython keeps sys.flags.debug at 0 unless -d is given. GraalPy was initializing that field from !PythonOptimizeFlag, so the default value was 1.

This change sets sys.flags.debug to 0 and adds a GraalPy unittest that asserts the default.

Fixes #1213

Test plan

  1. Add SysFlagsTests.test_debug_is_zero_by_default on unmodified upstream/master.
  2. mx --java-home=lookup:default python-jvm && mx --java-home=lookup:default graalpytest test_sys.py — fails (1 != 0).
  3. Set the debug field to 0 in SysModuleBuiltins.java.
  4. Rebuild and rerun test_sys.py — passes.
  5. Nearby sys tests: mx --java-home=lookup:default graalpytest test_sys.py test_sysconfig.py test_sys_settrace.py — passes.

Before (unmodified SysModuleBuiltins, new test only)

===== BEFORE (unmodified SysModuleBuiltins) =====
WARNING:   graalpython:PYTHON_NATIVE_STANDALONE_SVM_JAVA25:
distribution PYTHON_NATIVE_STANDALONE_SVM_JAVA25 redefined
Running: MX_GRAALPYTEST=1 PYTHONHASHSEED=0 /workspace/mxbuild/linux-amd64/GRAALPY_JVM_STANDALONE/bin/graalpy --vm.ea --python.WithJavaStacktrace=1 --experimental-options=true --python.EnableDebuggingBuiltins /workspace/graalpython/com.oracle.graal.python.test/src/runner.py run test_sys.py '--subprocess-args=--experimental-options=true --python.EnableDebuggingBuiltins' --append-path=/workspace/graalpython/lib-python/3
Collected 3 tests
graalpython/com.oracle.graal.python.test/src/tests/test_sys.py::tests.test_sys.SysFlagsTests.test_debug_is_zero_by_default ... FAIL (0.08s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys.py::tests.test_sys.WindowsVersionTests.test_getwindowsversion_java_backend ... skipped 'Windows only'
graalpython/com.oracle.graal.python.test/src/tests/test_sys.py::tests.test_sys.WindowsVersionTests.test_getwindowsversion_matches_os ... skipped 'Windows only'

======================================================================
FAIL: graalpython/com.oracle.graal.python.test/src/tests/test_sys.py::tests.test_sys.SysFlagsTests.test_debug_is_zero_by_default
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/workspace/graalpython/com.oracle.graal.python.test/src/tests/test_sys.py", line 141, in test_debug_is_zero_by_default
    self.assertEqual(sys.flags.debug, 0)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
AssertionError: 1 != 0

Ran 3 tests in 0.11s

FAILED (failures=1, skipped=2)
Command '/workspace/mxbuild/linux-amd64/GRAALPY_JVM_STANDALONE/bin/graalpy --vm.ea --python.WithJavaStacktrace=1 --experimental-options=true --python.EnableDebuggingBuiltins /workspace/graalpython/com.oracle.graal.python.test/src/runner.py run test_sys.py '--subprocess-args=--experimental-options=true --python.EnableDebuggingBuiltins' --append-path=/workspace/graalpython/lib-python/3' returned non-zero exit status 1.
===== BEFORE EXIT=1 =====

After (debug hardcoded to 0)

===== AFTER (debug hardcoded to 0) =====
WARNING:   graalpython:PYTHON_NATIVE_STANDALONE_SVM_JAVA25:
distribution PYTHON_NATIVE_STANDALONE_SVM_JAVA25 redefined
Running: MX_GRAALPYTEST=1 PYTHONHASHSEED=0 /workspace/mxbuild/linux-amd64/GRAALPY_JVM_STANDALONE/bin/graalpy --vm.ea --python.WithJavaStacktrace=1 --experimental-options=true --python.EnableDebuggingBuiltins /workspace/graalpython/com.oracle.graal.python.test/src/runner.py run test_sys.py '--subprocess-args=--experimental-options=true --python.EnableDebuggingBuiltins' --append-path=/workspace/graalpython/lib-python/3
Collected 3 tests
graalpython/com.oracle.graal.python.test/src/tests/test_sys.py::tests.test_sys.SysFlagsTests.test_debug_is_zero_by_default ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys.py::tests.test_sys.WindowsVersionTests.test_getwindowsversion_java_backend ... skipped 'Windows only'
graalpython/com.oracle.graal.python.test/src/tests/test_sys.py::tests.test_sys.WindowsVersionTests.test_getwindowsversion_matches_os ... skipped 'Windows only'

Ran 3 tests in 0.03s

OK (passed=1, skipped=2)
===== AFTER test_sys EXIT=0 =====

Nearby sys tests

===== NEARBY SYS TESTS =====
WARNING:   graalpython:PYTHON_NATIVE_STANDALONE_SVM_JAVA25:
distribution PYTHON_NATIVE_STANDALONE_SVM_JAVA25 redefined
Running: MX_GRAALPYTEST=1 PYTHONHASHSEED=0 /workspace/mxbuild/linux-amd64/GRAALPY_JVM_STANDALONE/bin/graalpy --vm.ea --python.WithJavaStacktrace=1 --experimental-options=true --python.EnableDebuggingBuiltins /workspace/graalpython/com.oracle.graal.python.test/src/runner.py run test_sys.py test_sysconfig.py test_sys_settrace.py '--subprocess-args=--experimental-options=true --python.EnableDebuggingBuiltins' --append-path=/workspace/graalpython/lib-python/3
Collected 52 tests
graalpython/com.oracle.graal.python.test/src/tests/test_sys.py::tests.test_sys.SysFlagsTests.test_debug_is_zero_by_default ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys.py::tests.test_sys.WindowsVersionTests.test_getwindowsversion_java_backend ... skipped 'Windows only'
graalpython/com.oracle.graal.python.test/src/tests/test_sys.py::tests.test_sys.WindowsVersionTests.test_getwindowsversion_matches_os ... skipped 'Windows only'
graalpython/com.oracle.graal.python.test/src/tests/test_sysconfig.py::test_sysconfig ... ok (0.01s)
graalpython/com.oracle.graal.python.test/src/tests/test_sysconfig.py::test_platform_sysconfigdata ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sysconfig.py::test_tzpath_searches_system_time_zones ... ok (3.06s)
graalpython/com.oracle.graal.python.test/src/tests/test_sysconfig.py::test_windows_libpython_is_not_exposed ... skipped 'Windows-specific sysconfig behavior'
graalpython/com.oracle.graal.python.test/src/tests/test_sysconfig.py::test_windows_hash_algorithm ... skipped 'Windows-specific sysconfig behavior'
graalpython/com.oracle.graal.python.test/src/tests/test_sysconfig.py::test_windows_library_names ... skipped 'Windows-specific sysconfig behavior'
graalpython/com.oracle.graal.python.test/src/tests/test_sysconfig.py::test_windows_platform_specific_sys_attributes ... skipped 'Windows-specific sysconfig behavior'
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.AnnotationsEvents.test_multiple_fun_annotations ... ok (0.16s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.AsyncTracingEventsUnitTest.test_01_await ... skipped 'GR-65570: GraalPy does not report await exception trace events yet.'
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.AsyncTracingEventsUnitTest.test_02_async_with ... skipped 'GR-65570: GraalPy does not report async with exception trace events yet.'
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.AsyncTracingEventsUnitTest.test_03_async_for ... skipped 'GR-65570: GraalPy does not match CPython async for trace events yet.'
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_01_except_star_with_name ... ok (0.01s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_02_except_star_multi_with_name ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_03_except_star_with_finally ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_04_test_try_except_star_with_wrong_type ... skipped 'TODO: Fix return in finally.'
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_05_if_false_in_try_except_star ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_06_try_in_try_with_exception ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_07_tracing_exception_raised_in_with ... skipped "TODO: Isn't even tagged from CPython tests."
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_08_try_except_star_no_exception ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_09_try_except_star_named_no_exception ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_10_try_except_star_exception_caught ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_11_try_except_star_named_exception_caught ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_12_try_except_star_exception_not_caught ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_13_try_except_star_named_exception_not_caught ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.ExceptStarTraceTest.test_14_try_except_star_nested ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.MultilineCallsTraceTest.test_01_multiline_call_method_basic ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.MultilineCallsTraceTest.test_02_multiline_call_method_vargs ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.MultilineCallsTraceTest.test_03_multiline_call_function_basic ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.MultilineCallsTraceTest.test_04_multiline_call_function_vargs ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.MultilineCallsTraceTest.test_05_multiline_call_function_fallback_to_vargs ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.MultilineCallsTraceTest.test_06_multiline_binop ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.MultilineCallsTraceTest.test_07_multiline_boolop ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.MultilineCallsTraceTest.test_08_multiline_boolop_short ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.SingleLineMultipleStmts.test_01_if_elif_else ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.SingleLineMultipleStmts.test_02_if_elif_else_implicit_return ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTests.test_01_basic ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTests.test_02_more_complex ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTests.test_04_two_functions ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTests.test_05_generator_example ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTests.test_05_generator_same_line_example ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTests.test_06_f_trace_preserved ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTests.test_07_async_actions_not_traced ... ok (0.06s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTests.test_08_frame_f_trace_deletable ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTestsStmtTry.test_01_reraise ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTestsStmtWith.test_01_break_in_with ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTestsStmtWith.test_02_if_false_in_with_multiple_nested ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTestsStmtWith.test_03_break_in_with_nested ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTestsStmtWith.test_04_except_in_with ... ok (0.00s)
graalpython/com.oracle.graal.python.test/src/tests/test_sys_settrace.py::tests.test_sys_settrace.TraceTestsStmtWith.test_05_except_in_with_nested ... ok (0.00s)

Ran 52 tests in 3.45s

OK (passed=41, skipped=11)
===== NEARBY EXIT=0 =====

This change was prepared with AI assistance. I remain responsible for the contribution and have reviewed it.

@hippi345
Set sys.flags.debug to 0 by default
fd65f63 
CPython reports sys.flags.debug as 0 unless -d is given. GraalPy
was setting it from the inverse of PythonOptimizeFlag, so the
default value was 1.

Fixes oracle#1213

Signed-off-by: hippi345 <13539685+hippi345@users.noreply.github.com>
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[Bug]: sys.flags.debug is 1 whenever optimization is off

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