PyRun_InteractiveLoopFlags() only stops if PyRun_InteractiveOneFlags() returns E_EOF. But PyRun_InteractiveOneFlags() if an error occurs:
 - sys.stdin has no encoding attribute
 - PyArena_New() returns NULL
 - PyParser_ASTFromFile() returns NULL
 - PyImport_AddModule("__main__") returns NULL
 - run_mod() returns NULL

You can reproduce the error by adding the followg line to the end of Lib/site.py:

  sys.stdin = object()

Attached patch is for py3k, but the bug does also exist in trunk.

PyRun_InteractiveLoop() doesn't specify the possible return value. It's maybe because it's always zero and that the error are not handled :-)
http://docs.python.org/c-api/veryhigh.html#PyRun_InteractiveLoop

PyRun_InteractiveOneFlags() documentation is also wrong: the result can only be: 0 (succes), -1 (exception raised) or E_EOF (=11, end of file).

I just hit this one myself, and was about to write a bug and patch.

On reviewing the patch:

1. This really has the same issue as the original code: it detects one of a few known return values, and will infinitely loop on an unexpected return value.  It would be better to explicitly check for 0 (continue), E_EOF (exit normally), and any other result (exit abnormally).

2. I don't think you want to unconditionally call PyErr_Print(), because you don't know for sure that an exception is set.

3. Returning 0 from PyRun_InteractiveLoopFlags() when an error occurs is a behavior change, which makes its documentation incorrect (meaning there should also be a doc patch). But to be honest, I don't think it's correct to return 0 in this case. It seems better to return the actual error code (which also requires a doc patch)

If you don't have time to update the patch, let me know and I'll put one together.

I don't have time to write a better patch, please improve mine :-)

tlesher> If you don't have time to update the patch, let me know and I'll put one together.

I would be happy if you write a new patch :-)

Issue #11730 has been marked as duplicate.

I'd prefer not exit program but try to use Py_FileSystemDefaultEncoding as enc when sys.stdin is invalid. On most cases, setting sys.stdin to some other invalid value does means the program could not continue running.

> On most cases, setting sys.stdin to some other invalid value does means the program could not continue running.


Sorry, it should be:

On most cases, setting sys.stdin to some other invalid value does not mean the program could not continue running.

Victor: would you object to ysj.ray's solution? 

I don't think it was an option when we last looked at this issue.

Updated patch:  use Py_FileSystemDefaultEncoding (if possible) when sys.stdin is (or becomes) invalid; if none, then fails without entering infinite loop. Docs for PyRun_InteractiveLoopFlags have been updated.

Corrected const warning in previous patch.