MutaFix run: boltons-005

ranker nvidia/NVIDIA-Nemotron-3-Nano-30B-A3B · patcher nvidia/nemotron-3-super-120b-a12b · via Nebius Token Factory

fixedoutcome
16swall time
3model calls
$0.0021API cost
Benchmark ground truth (hidden from the agent)
boltons/tbutils.py:647 · operator NEGCOND · function boltons/tbutils.py::print_exception
- if not (file is None):   (injected bug)+ if file is None:   (original)
retriever rank 1 of 20 · ranker position 1 · patched the right function yes · exact restore yes

Trace

reproduce
+2.97s
1 failing test(s) · 1 failed, 524 passed · 2.97s
failing tests and errors
tests/test_tbutils.py::test_exception_info
tests/test_tbutils.py::test_exception_info
E   AssertionError: assert 'ValueError: yay fun' in ''
trace
+3.39s
re-ran 1 test file(s) with the trace plugin: 1 failing and 1 passing tests, 18 library functions ran in a failing test · 0.28s
tests/test_tbutils.py
retrieve
+3.39s
923 functions indexed, 90 reachable from tests/test_tbutils.py::test_exception_info in the static call graph. Kept 20 candidates, ranked by spectrum score (Ochiai), call graph and BM25 break ties.
candidates in retriever order
  1. boltons/tbutils.py::print_exception call depth 1 · Ochiai 1.00 (failing 1, passing 0)
  2. boltons/tbutils.py::fix_print_exception call depth 1 · Ochiai 1.00 (failing 1, passing 0)
  3. boltons/tbutils.py::TracebackInfo.__str__ call depth 1 · Ochiai 1.00 (failing 1, passing 0)
  4. boltons/tbutils.py::format_exception_only call depth 2 · Ochiai 1.00 (failing 1, passing 0)
  5. boltons/tbutils.py::_format_final_exc_line call depth 3 · Ochiai 1.00 (failing 1, passing 0)
  6. boltons/tbutils.py::ExceptionInfo.from_exc_info call depth 1 · Ochiai 0.71 (failing 1, passing 1)
  7. boltons/tbutils.py::TracebackInfo.from_traceback call depth 1 · Ochiai 0.71 (failing 1, passing 1)
  8. boltons/tbutils.py::ExceptionInfo.from_current call depth 1 · Ochiai 0.71 (failing 1, passing 1)
  9. boltons/tbutils.py::Callpoint.tb_frame_str call depth 1 · Ochiai 0.71 (failing 1, passing 1)
  10. boltons/tbutils.py::ExceptionInfo.__init__ call depth 1 · Ochiai 0.71 (failing 1, passing 1)
  11. boltons/tbutils.py::TracebackInfo.__init__ call depth 1 · Ochiai 0.71 (failing 1, passing 1)
  12. boltons/tbutils.py::TracebackInfo.get_formatted call depth 2 · Ochiai 0.71 (failing 1, passing 1)
  13. boltons/tbutils.py::Callpoint.from_tb call depth 2 · Ochiai 0.71 (failing 1, passing 1)
  14. boltons/tbutils.py::_some_str call depth 2 · Ochiai 0.71 (failing 1, passing 1)
  15. boltons/tbutils.py::_DeferredLine.__len__ call depth 3 · Ochiai 0.71 (failing 1, passing 1)
  16. boltons/tbutils.py::_DeferredLine.__str__ call depth 3 · Ochiai 0.71 (failing 1, passing 1)
  17. boltons/tbutils.py::_DeferredLine.__init__ call depth 3 · Ochiai 0.71 (failing 1, passing 1)
  18. boltons/tbutils.py::Callpoint.__init__ call depth - · Ochiai 0.71 (failing 1, passing 1)
  19. boltons/tbutils.py::ExceptionInfo.__repr__ call depth 1 · Ochiai 0.00 (failing 0, passing 0)
  20. boltons/tbutils.py::Callpoint.from_current call depth 1 · Ochiai 0.00 (failing 0, passing 1)
rank
+3.39s
spectrum order kept (no model call)
  1. boltons/tbutils.py::print_exception
  2. boltons/tbutils.py::fix_print_exception
  3. boltons/tbutils.py::TracebackInfo.__str__
  4. boltons/tbutils.py::format_exception_only
  5. boltons/tbutils.py::_format_final_exc_line
read
+5.3s
turn 1 · NVIDIA-Nemotron-3-Nano-30B-A3B · 2810 in / 109 out · 1.91s · $0.00019

read boltons/tbutils.py::print_exception

The test failure indicates that the exception message 'ValueError: yay fun' is not appearing in the output of print_exception. Looking at the print_exception function, it prints the traceback info (tbi) first and then formats the exception value using format_exception_only. The issue is likely in how the exception value is formatted or printed. I need to examine the print_exception function to see how it handles the exception value printing.

patch
+8.37s
turn 2 · NVIDIA-Nemotron-3-Nano-30B-A3B · 3300 in / 236 out · 2.77s · $0.00025

The print_exception function looks correct. It prints the traceback info and then iterates through format_exception_only to print each line of the exception formatting. The issue might be elsewhere. Let me check if there's an issue with how the exception value is being processed in format_exception_only or if there's a problem with the order of operations. I'll look at the format_exception_only function next.

tests: 1 failing (target tests) 1 failed
tests/test_tbutils.py::test_exception_info
patch
+16.13s
turn 3 · nemotron-3-super-120b-a12b · 3615 in / 622 out · 4.11s · $0.00164
The condition for setting the default file stream was inverted. When a file parameter was provided (like fake_stderr2 in the test), the code was incorrectly overriding it with sys.stderr. This caused the exception output to go to the wrong stream, making it appear empty in the test's captured output. The fix ensures we only set file to sys.stderr when file is actually None.
--- a/boltons/tbutils.py+++ b/boltons/tbutils.py@@ -645,5 +645,5 @@     """ -    if not (file is None):+    if file is None:         file = sys.stderr     if tb:
tests: all tests pass 525 passed
model reasoning (excerpt)
Let me re-examine the print_exception function more carefully. I notice something suspicious:

In the function:
```python
def print_exception(etype, value, tb, limit=None, file=None):
    ...
    if not (file is None):
        file = sys.stderr
    if tb:
        tbi = TracebackInfo.from_traceback(tb, limit)
        print(str(tbi), end='', file=file)

    for line in format_exception_only(etype, value):
        print(line, end='', file=file)
```

There's a logic error! The condition `if not (file is None):` means "if file is NOT None", then set `file = sys.stderr`. But that's backwards! If file is provided (not None), we should use that file, not override it with sys.stderr.

It should be:
```python
if file is None:
    file = sys.stderr
```

But currently it's:
```python
if not (file is None):  # if file is NOT None
    file = sys.stderr   # then set it to stderr (overriding the provided file!)
```

This means that whenever a file parameter is provided (like fake_stderr2 in the test), it gets overridden to sys.stderr, so the output goes to the wrong place!

Let me verify this is indeed the bug by looking at the test again:
- fake_stderr2 = StringIO()
- sys.stderr = fake_stderr1
- print_exception(*sys.exc_info(), file=fake_stderr2)

So when print_exception is called with file=fake_stderr2, the current code does:
- if not (fake_stderr2 is None):  # This is True
-     file = sys.stderr           # So file becomes sys.stderr (which is fake_stderr1 due to the earlier assignment)

Final patch
--- a/boltons/tbutils.py+++ b/boltons/tbutils.py@@ -645,5 +645,5 @@     """ -    if not (file is None):+    if file is None:         file = sys.stderr     if tb: