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fix(regression): support embedded submodule #5650

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fix(regression): support embedded submodule #5650

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e6f029c
tests: add test for embedded submodule
henryiii May 9, 2025
69dc30a
tests: adjust
henryiii May 9, 2025
cd72edf
Update test_interpreter.cpp
henryiii May 9, 2025
edefef4
Update test_interpreter.cpp
henryiii May 9, 2025
c22a5b8
Update test_interpreter.cpp
henryiii May 9, 2025
a8bbfd3
Update test_interpreter.cpp
henryiii May 9, 2025
96c7daa
Update pybind11.h
henryiii May 9, 2025
1972a8a
fix: end instead of endif
henryiii May 10, 2025
e922cc5
Update include/pybind11/pybind11.h
henryiii May 10, 2025
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11 changes: 8 additions & 3 deletions include/pybind11/pybind11.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1342,13 +1342,18 @@ class module_ : public object {
// GraalPy doesn't support PyModule_GetFilenameObject,
// so getting by attribute (see PR #5584)
handle this_module = m_ptr;
result.attr("__file__") = this_module.attr("__file__");
if (object this_file = getattr(this_module, "__file__", none())) {
result.attr("__file__") = this_file;
}
#else
handle this_file = PyModule_GetFilenameObject(m_ptr);
if (!this_file) {
if (this_file) {
result.attr("__file__") = this_file;
} else if (PyErr_ExceptionMatches(PyExc_SystemError) != 0) {
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Ugh ... if we have to catch a SystemError here to accommodate submodules, I regret posting this comment on PR #5584.

I think it'll be best to get rid of this #else branch then.

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Python even throws exceptions when iterating over ranges. I would expect Python's low level C error handling to be more lightweight (if one can say that when it comes to python) than what happens if this were translated to a C++ exception.

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It should be extremely rare, this is only for embedded submodules, normally it works. I think it's probably fine to leave this way.

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Up to you, I'm OK if you want to keep it.

What still makes me feel uneasy: the risk of masking unexpected SystemErrors.

Which is of course extremely low, but not zero. (Google experience: anything that can happen, does happen.)

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The function is part of the Stable API and just accesses a dictionary. My two cents: the current implementation is safe.

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Do you have a link to the implementation handy?

What's on my mind: Why does it raise SystemError, and not AttributeError?

I'd feel more cozy ignoring an AttributeError.

But as I said, I'm fine with this.

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The function explicitly sets the system error. I could not see any system errors in the source of the dictionary.

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Thanks!

The function explicitly sets the system error.

Seems like an unfortunate choice, to have it in the same class of exceptions as e.g. out-of-memory, but 🤷

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>>> SystemError.__mro__
(<class 'SystemError'>, <class 'Exception'>, <class 'BaseException'>, <class 'object'>)
>>> MemoryError.__mro__
(<class 'MemoryError'>, <class 'Exception'>, <class 'BaseException'>, <class 'object'>)

https://docs.python.org/3/library/exceptions.html#SystemError

Raised when the interpreter finds an internal error, but the situation does not look so serious to cause it to abandon all hope.

Doesn’t seem too bad, I think it’s for things like this, exceptions that shouldn’t make it up to the user.

PyErr_Clear();
} else {
throw error_already_set();
}
result.attr("__file__") = this_file;
#endif
attr(name) = result;
return result;
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6 changes: 6 additions & 0 deletions tests/test_embed/test_interpreter.cpp
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Expand Up @@ -61,6 +61,9 @@ PYBIND11_EMBEDDED_MODULE(widget_module, m) {
.def_property_readonly("the_message", &Widget::the_message);

m.def("add", [](int i, int j) { return i + j; });

auto sub = m.def_submodule("sub");
sub.def("add", [](int i, int j) { return i + j; });
}

PYBIND11_EMBEDDED_MODULE(trampoline_module, m) {
Expand Down Expand Up @@ -316,6 +319,9 @@ TEST_CASE("Restart the interpreter") {
auto cpp_module = py::module_::import("widget_module");
REQUIRE(cpp_module.attr("add")(1, 2).cast<int>() == 3);

// Also verify submodules work
REQUIRE(cpp_module.attr("sub").attr("add")(1, 41).cast<int>() == 42);

// C++ type information is reloaded and can be used in python modules.
auto py_module = py::module_::import("test_interpreter");
auto py_widget = py_module.attr("DerivedWidget")("Hello after restart");
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