Traceback leaks global code when `exec`:ed code raises
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Description
Bug report
Bug description:
Details
The traceback module's various functions for inspecting an exception leaks surrounding code when used to inspect an exception originating from an exec or eval call. I discovered this using traceback.format_exception but it applies to traceback.print_exc and the other ones that call or are called by those as well.
Specifically when compiled for "exec" mode using compile, and the exec:ed code inherits the context from which exec was called.
In this example, the comment on the first line is included in the printed traceback.
# Hi, I'm in the error message
import traceback
try:
exec(compile("tuple()[0]", "s", "exec"))
except:
traceback.print_exc()
This prints:
Traceback (most recent call last):
File "<filename>", line 4, in <module>
exec(compile("tuple()[0]", "s", "exec"))
File "s", line 1, in <module>
# Hi, I'm in the error message
IndexError: tuple index out of range
It seems that whatever line number the error is on in the exec:ed code is applied to the calling file instead of the exec:ed code.
Changing line 4 in the example above to exec("tuple()[0]") avoids the issue, and no info regarding the line is printed by traceback. This behavior is in line with what python outputs when the exception is not caught:
# Hi, I'm not in the error message
exec(compile("tuple()[0]", "s", "exec"))
results in:
Traceback (most recent call last):
File "<filename>", line 2, in <module>
exec(compile("tuple()[0]", "s", "exec"))
File "s", line 1, in <module>
IndexError: tuple index out of range
Summary
Example code
# Hi, I'm in the error message
import traceback
try:
exec(compile("tuple()[0]", "s", "exec"))
except:
traceback.print_exc()
Expected behaviour
Should print the following:
Traceback (most recent call last):
File "<filename>", line 4, in <module>
exec(compile("tuple()[0]", "s", "exec"))
File "s", line 1, in <module>
IndexError: tuple index out of range
Actual behaviour
Prints this:
Traceback (most recent call last):
File "<filename>", line 4, in <module>
exec(compile("tuple()[0]", "s", "exec"))
File "s", line 1, in <module>
# Hi, I'm in the error message
IndexError: tuple index out of range
CPython versions tested on:
3.8, 3.10, 3.11, 3.12
Operating systems tested on:
Linux, Windows
Linked PRs
- gh-122126
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the example with traceback.format_exception and traceback.print_exc, comparing compiled exec code with direct exec and uncaught exceptions. Trace how traceback rendering uses the filename and line number for the exec frame; done means the expected output omits the caller's source line, including for the other traceback functions described.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- backend
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 25/100