traceback._compute_suggestion_error crashes on __getattr__ raising

Bug report

Bug description:

This is a regression introduced in 3.13 because the new pyrepl. 3.14 is also affected.

Type this in an interactive 3.13/3.14 session:

>>> class a:
...     def __getattr__(self, x):
...         print(x)
...         print(qq)
...         
>>> b=a()
>>> b.pepe
pepe
qq
qq
Traceback (most recent call last):
  File "<python-input-5>", line 1, in <module>
  File "<python-input-3>", line 4, in __getattr__
NameError: name 'qq' is not defined

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/usr/local/lib/python3.13/_pyrepl/__main__.py", line 6, in <module>
    __pyrepl_interactive_console()
  File "/usr/local/lib/python3.13/_pyrepl/main.py", line 59, in interactive_console
    run_multiline_interactive_console(console)
  File "/usr/local/lib/python3.13/_pyrepl/simple_interact.py", line 160, in run_multiline_interactive_console
    more = console.push(_strip_final_indent(statement), filename=input_name, _symbol="single")  # type: ignore[call-arg]
  File "/usr/local/lib/python3.13/code.py", line 314, in push
    more = self.runsource(source, filename, symbol=_symbol)
  File "/usr/local/lib/python3.13/_pyrepl/console.py", line 211, in runsource
    self.runcode(code)
  File "/usr/local/lib/python3.13/code.py", line 96, in runcode
    self.showtraceback()
  File "/usr/local/lib/python3.13/code.py", line 129, in showtraceback
    self._showtraceback(typ, value, tb.tb_next, '')
  File "/usr/local/lib/python3.13/code.py", line 145, in _showtraceback
    self._excepthook(typ, value, tb)
  File "/usr/local/lib/python3.13/_pyrepl/console.py", line 169, in _excepthook
    lines = traceback.format_exception(
  File "/usr/local/lib/python3.13/traceback.py", line 154, in format_exception
    te = TracebackException(type(value), value, tb, limit=limit, compact=True)
  File "/usr/local/lib/python3.13/traceback.py", line 1090, in __init__
    suggestion = _compute_suggestion_error(exc_value, exc_traceback, wrong_name)
  File "/usr/local/lib/python3.13/traceback.py", line 1516, in _compute_suggestion_error
    if hasattr(self, wrong_name):
  File "<python-input-3>", line 4, in __getattr__
NameError: name 'qq' is not defined

And the interactive python session is terminated.

Under previous Python releases, with no pyrepl, the right exception is raised and the repl keeps going:

Python 3.9.21 (main, Dec  9 2024, 19:43:35) 
[GCC 10.5.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> class a:
...   def __getattr__(self, x):
...     print(x)
...     print(qq)
... 
>>> b=a()
>>> b.pepe
pepe
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in __getattr__
NameError: name 'qq' is not defined
>>>

Notice that this problem raises SPECIFICALLY if __getattr__ raises a NameError exception. Other exceptions, like division by zero, don't break pyrepl.

CPython versions tested on:

3.13, 3.12, 3.11, 3.10, 3.9, 3.14

Operating systems tested on:

Linux

Linked PRs

A quick fix (I'm not sure it's a right way):

diff --git a/Lib/traceback.py b/Lib/traceback.py
index 31c73efcef..abcc099c29 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -1520,8 +1520,11 @@ def _compute_suggestion_error(exc_value, tb, wrong_name):
         # has the wrong name as attribute
         if 'self' in frame.f_locals:
             self = frame.f_locals['self']
-            if hasattr(self, wrong_name):
-                return f"self.{wrong_name}"
+            try:
+                if hasattr(self, wrong_name):
+                    return f"self.{wrong_name}"
+            except NameError:
+                pass
 
     try:
         import _suggestions

>>> b.pepe
pepe
qq
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    b.pepe
  File "<python-input-0>", line 4, in __getattr__
    print(qq)
          ^^
NameError: name 'qq' is not defined

Cool, but "qq" should not be searched in the class. Notice that __getattr__ is called twice, first for "pepe" and another one, incorrectly, for "qq".

That might be helpful for suggestions, see 99e2e60.

Merge branch 'main' into pythongh-129605

Another instance of the same error:

import traceback


class C:
    @property
    def foo(self):
        return foo

try:
    C().foo
except Exception:
    print(traceback.format_exc())

gives (at least on Python 3.12):

% python t.py
Traceback (most recent call last):
  File "/Users/konstantin/t.py", line 10, in <module>
    C().foo
  File "/Users/konstantin/t.py", line 7, in foo
    return foo
           ^^^
NameError: name 'foo' is not defined

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/konstantin/t.py", line 12, in <module>
    print(traceback.format_exc())
          ^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.12/3.12.6/Frameworks/Python.framework/Versions/3.12/lib/python3.12/traceback.py", line 184, in format_exc
    return "".join(format_exception(sys.exception(), limit=limit, chain=chain))
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.12/3.12.6/Frameworks/Python.framework/Versions/3.12/lib/python3.12/traceback.py", line 139, in format_exception
    te = TracebackException(type(value), value, tb, limit=limit, compact=True)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.12/3.12.6/Frameworks/Python.framework/Versions/3.12/lib/python3.12/traceback.py", line 767, in __init__
    suggestion = _compute_suggestion_error(exc_value, exc_traceback, wrong_name)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.12/3.12.6/Frameworks/Python.framework/Versions/3.12/lib/python3.12/traceback.py", line 1100, in _compute_suggestion_error
    if hasattr(self, wrong_name):
       ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/konstantin/t.py", line 7, in foo
    return foo
           ^^^
NameError: name 'foo' is not defined

so the property gets re-executed. In other cases this can also lead to an infinite chain of exceptions.

I encountered this bug when trying to log such an exception using logging.

The following code demonstrates the issue (using ValueError for demonstration purposes, even though the real issue I had was a NameError due to forgetting to write self.).

import logging

class Foo:
    @property
    def x(self):
        raise ValueError("x")

    def y(self):
        return x

logger = logging.getLogger(__name__)

try:
    Foo().y()
except Exception as e:
    logger.exception("y failed") # raises!

print("done") # not reached!

logger.exception prints "--- Logging error ---" and then calls traceback.print_exception which fails to print the traceback. The exception raised by hasattr is propagated by logger.exception, preventing the program from continuing!

I think this should be considered a bug in logging: logger.exception should probably silently drop any exceptions raised while trying to handle logging errors instead of propagating the exceptions.

This cannot be reproduced in v3.14: bisection confirms it was fixed in 641253c, for #132385. We can probably close this.

Looks valid in the master:

Python 3.15.0a0 (heads/main-dirty:2b0c684e07, Jun 13 2025, 06:46:26) [Clang 14.0.6 ] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> class a:
...     def __getattr__(self, x):
...         print(x)
...         print(qq)
...         
... b=a()
... 
>>> b.pepe
pepe
qq
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    b.pepe
  File "<python-input-0>", line 4, in __getattr__
    print(qq)
          ^^
NameError: name 'qq' is not defined
>>>

Current Python 3.13.8 and 3.14.0 are not crashing anymore. I close this issue.

I found another way to reproduce this bug that still works in 3.14.4. PR #129632's approach of wrapping the NameError branch in try/except Exception: return None would fix this.

Here's the real-world reproducer (and how I came across this bug). Create a marimo (0.23.8) notebook with the following cell (that imports statsmodel 0.14.6, which in turn imports patsy 1.0.2).

import polars as pl
import statsmodels.formula.api as smf

df = pl.DataFrame({"a2": range(10), "b": range(10, 20)})
model = smf.ols(
    "a ~ b",
    data=df.to_pandas(),
)

The CPython process running the marimo kernel will crash when the cell is run. A misspelled column name in a formula string triggers a NameError inside patsy's eval() call (where f_locals is a live VarLookupDict). Marimo calls traceback.print_exception directly from Python to format cell errors — unlike the REPL, which uses C-level PyErr_Display and is robust to this — so the KeyError(0) propagates uncaught and kills the notebook kernel.

This minimal reproducer mocks patsy's VarLookupDict, which implements __getitem__ but not __iter__, causing Python to fall back to the legacy sequence protocol (__getitem__(0), __getitem__(1), ...) and immediately raise KeyError(0):

import traceback

class LegacyMapping:
    """Minimal repro of patsy.eval.VarLookupDict — implements __getitem__ but not __iter__."""
    def __getitem__(self, key):
        if key == "x":
            return 1
        raise KeyError(key)  # raises KeyError for integer keys too

try:
    eval("nonexistent_var", {}, LegacyMapping())
except NameError as e:
    traceback.print_exception(e)
    # Expected: prints NameError cleanly
    # Actual (3.13+): KeyError: 0 propagates out of print_exception

gh-129605: Add more exception handling when computing suggestions in …

[3.15] gh-129605: Add more exception handling when computing suggesti…

[3.14] gh-129605: Add more exception handling when computing suggesti…

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traceback._compute_suggestion_error crashes on `getattr` raising #129605

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Operating systems tested on:

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traceback._compute_suggestion_error crashes on __getattr__ raising #129605

Description

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

Linked PRs

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skirpichev commented on Feb 3, 2025

jcea commented on Feb 3, 2025

skirpichev commented on Feb 3, 2025

lopuhin commented on Feb 25, 2025

kak-0 commented on Apr 14, 2025

duaneg commented on Jun 13, 2025

skirpichev commented on Jun 13, 2025

jcea commented on Nov 11, 2025

shenker commented on May 30, 2026

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traceback._compute_suggestion_error crashes on `getattr` raising #129605