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gh-137576: Fix for Basic REPL Showing Incorrect Code in Tracebacks with PYTHONSTARTUP #137625

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gh-137576: Fix for Basic REPL Showing Incorrect Code in Tracebacks with PYTHONSTARTUP #137625

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@adqm adqm commented Aug 11, 2025 •
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This patch attempts to fix #137576 by changing the way interactive_filename is computed for the basic REPL to make sure that it always begins with < and ends with > so that doesn't get an entry in linecache.cache (which was causing the source from PYTHONSTARTUP to be used instead of the interactive input when generating tracebacks).

Updated behavior:

$ echo "print('hello from PYTHONSTARTUP')" > /tmp/foo.py
$ PYTHON_BASIC_REPL=1 PYTHONSTARTUP=/tmp/foo.py ./python
Python 3.15.0a0 (heads/basic_repl_error_reporting:3d46e8feed, Aug 10 2025, 21:12:17) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
hello from PYTHONSTARTUP
>>> 1/0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    1/0
    ~^~
ZeroDivisionError: division by zero

$ echo "def foo(x):  return 1/x" > /tmp/foo.py
$ PYTHON_BASIC_REPL=1 PYTHONSTARTUP=/tmp/foo.py ./python
Python 3.15.0a0 (heads/basic_repl_error_reporting:3d46e8feed, Aug 10 2025, 21:12:17) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> def bar(x):
...     return foo(x)
... 
>>> bar(0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    bar(0)
    ~~~^^^
  File "<stdin>", line 2, in bar
    return foo(x)
  File "/tmp/foo.py", line 1, in foo
    def foo(x):  return 1/x
                        ~^~
ZeroDivisionError: division by zero

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adqm commented Aug 11, 2025 •
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My original patch here also caused the tracebacks to report the filename as <stdin-N> instead of <stdin>. I think there's something nice about that (from the REPL, it's nice to see when the sources shown in the traceback came from different interactive inputs, better symmetry with pyrepl's reporting, etc.), but for now I added a commit to keep the reported filename as <stdin>.

Eclips4
Eclips4 approved these changes Aug 11, 2025
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Thank you!
A couple of nits.

Python/pythonrun.c
if (len >= 2
&& PyUnicode_ReadChar(filename, 0) == '<'
&& PyUnicode_ReadChar(filename, len - 1) == '>') {
PyObject *middle = PyUnicode_Substring(filename, 1, len-1);
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Could you please add error checks for PyUnicode_Substring, since it could return NULL?
If that happens, simply return NULL.
Also, in run_mode, please add an error check for when get_interactive_filename returns NULL (just propagate that NULL).

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Thanks for the review!

Could you please add error checks for PyUnicode_Substring, since it could return NULL?

Yep, I added a check there.

Also, in run_mode, please add an error check for when get_interactive_filename returns NULL (just propagate that NULL).

I think this one is already handled, on lines 1406-1408 (which happen just after get_interactive_filename is called).

        if (interactive_filename == NULL) {
            return NULL;
        }

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@Eclips4 Eclips4 Eclips4 approved these changes

@ericsnowcurrently ericsnowcurrently Awaiting requested review from ericsnowcurrently ericsnowcurrently is a code owner

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traceback shows wrong source code in basic REPL when PYTHONSTARTUP is set
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@adqm @Eclips4