embed.h Python 3.11 config.use_environment=1 + PYTHONPATH test (#4119)

* Add debug fprintf to test_interpreter.cpp

* Update `sys.path` from `PYTHONPATH` in Python >= 3.11 branch of `initialize_interpreter()`

* Use `config.isolated = 0; config.use_environment = 1;`

As suggsted by @vstinner here: #4119 (comment)

* Add `TEST_CASE("PYTHONPATH is used to update sys.path")`

* Fix clang-tidy error.

* Use `_putenv_s()` under Windows.

* Fix clang-tidy error: argument name ... in comment does not match parameter name

* Remove slash from PYTHONPATH addition, to work around Windows slash-vs-backslash issue.

* Use `py::str(...)` instead of `.attr("__str__")` as suggested by @Skylion007

Co-authored-by: Aaron Gokaslan <[email protected]>

Co-authored-by: Aaron Gokaslan <[email protected]>

Author: rwgk

include/pybind11/embed.h

@@ -150,6 +150,8 @@ inline void initialize_interpreter(bool init_signal_handlers = true,
 #else
     PyConfig config;
     PyConfig_InitIsolatedConfig(&config);
+    config.isolated = 0;
+    config.use_environment = 1;
     config.install_signal_handlers = init_signal_handlers ? 1 : 0;
 
     PyStatus status = PyConfig_SetBytesArgv(&config, argc, const_cast<char *const *>(argv));

tests/test_embed/catch.cpp

@@ -20,7 +20,25 @@
 namespace py = pybind11;
 
 int main(int argc, char *argv[]) {
+    // Setup for TEST_CASE in test_interpreter.cpp, tagging on a large random number:
+    std::string updated_pythonpath("pybind11_test_embed_PYTHONPATH_2099743835476552");
+    const char *preexisting_pythonpath = getenv("PYTHONPATH");
+    if (preexisting_pythonpath != nullptr) {
+#if defined(_WIN32)
+        updated_pythonpath += ';';
+#else
+        updated_pythonpath += ':';
+#endif
+        updated_pythonpath += preexisting_pythonpath;
+    }
+#if defined(_WIN32)
+    _putenv_s("PYTHONPATH", updated_pythonpath.c_str());
+#else
+    setenv("PYTHONPATH", updated_pythonpath.c_str(), /*replace=*/1);
+#endif
+
     py::scoped_interpreter guard{};
+
     auto result = Catch::Session().run(argc, argv);
 
     return result < 0xff ? result : 0xff;

tests/test_embed/test_interpreter.cpp

@@ -75,6 +75,13 @@ PYBIND11_EMBEDDED_MODULE(throw_error_already_set, ) {
     d["missing"].cast<py::object>();
 }
 
+TEST_CASE("PYTHONPATH is used to update sys.path") {
+    // The setup for this TEST_CASE is in catch.cpp!
+    auto sys_path = py::str(py::module_::import("sys").attr("path")).cast<std::string>();
+    REQUIRE_THAT(sys_path,
+                 Catch::Matchers::Contains("pybind11_test_embed_PYTHONPATH_2099743835476552"));
+}
+
 TEST_CASE("Pass classes and data between modules defined in C++ and Python") {
     auto module_ = py::module_::import("test_interpreter");
     REQUIRE(py::hasattr(module_, "DerivedWidget"));