Raise during unsupported model imports

We can't import multiple extensions with the same name.
Raise if this is attempted.

Related to #1936.

python/sdist/amici/__init__.py

@@ -11,6 +11,7 @@
 import os
 import re
 import sys
+import sysconfig
 from pathlib import Path
 from types import ModuleType as ModelModule
 from typing import Any
@@ -140,8 +141,7 @@ def get_model(self) -> amici.Model:
             """Create a model instance."""
             ...
 
-        def get_jax_model(self) -> JAXModel:
-            ...
+        def get_jax_model(self) -> JAXModel: ...
 
     AmiciModel = Union[amici.Model, amici.ModelPtr]
 
@@ -183,8 +183,42 @@ def import_model_module(
         raise ValueError(f"module_path '{module_path}' is not a directory.")
 
     module_path = os.path.abspath(module_path)
+    ext_suffix = sysconfig.get_config_var("EXT_SUFFIX")
+    ext_mod_name = f"{module_name}._{module_name}"
 
     # module already loaded?
+    if (m := sys.modules.get(ext_mod_name)) and m.__file__.endswith(
+        ext_suffix
+    ):
+        # this is the c++ extension we can't unload
+        loaded_file = Path(m.__file__)
+        needed_file = Path(
+            module_path,
+            module_name,
+            f"_{module_name}{ext_suffix}",
+        )
+        if not loaded_file.samefile(needed_file):
+            # this is not the right module, and we can't unload it
+            raise RuntimeError(
+                f"Cannot import extension for {module_name} from "
+                f"{module_path}, because an extension with the same name was "
+                f"has already been imported from {loaded_file.parent}. "
+                "Import the module with a different name or restart the "
+                "Python kernel."
+            )
+        # this is the right file, but did it change on disk?
+        t_imported = m.get_import_time()
+        t_modified = os.path.getmtime(m.__file__)
+        if t_imported < t_modified:
+            raise RuntimeError(
+                f"Cannot import extension for {module_name} from "
+                f"{module_path}, because an extension in the same location "
+                f"has already been imported, but the file was modified on "
+                "disk. Import the module with a different name or restart the "
+                "Python kernel."
+            )
+
+    # unlike extension modules, Python modules can be unloaded
     if module_name in sys.modules:
         # if a module with that name is already in sys.modules, we remove it,
         # along with all other modules from that package. otherwise, there

python/tests/test_sbml_import.py

@@ -773,3 +773,48 @@ def test_constraints():
                 amici_solver.getAbsoluteTolerance(),
             )
         )
+
+
+@skip_on_valgrind
+def test_same_extension_warning():
+    """Test for error when loading a model with the same extension name as an
+    already loaded model."""
+    from amici.antimony_import import antimony2amici
+
+    ant_model_1 = """
+    model test_same_extension_warning
+        species A = 0
+        p = 1
+        A' = p
+    end
+    """
+    ant_model_2 = ant_model_1.replace("1", "2")
+
+    module_name = "test_same_extension"
+    with TemporaryDirectory(prefix=module_name, delete=False) as outdir:
+        antimony2amici(
+            ant_model_1,
+            model_name=module_name,
+            output_dir=outdir,
+            compute_conservation_laws=False,
+        )
+        model_module_1 = amici.import_model_module(
+            module_name=module_name, module_path=outdir
+        )
+        assert model_module_1.get_model().getParameters()[0] == 1.0
+        # no error if the same model is loaded again without changes on disk
+        model_module_1 = amici.import_model_module(
+            module_name=module_name, module_path=outdir
+        )
+        assert model_module_1.get_model().getParameters()[0] == 1.0
+        antimony2amici(
+            ant_model_2,
+            model_name=module_name,
+            output_dir=outdir,
+            compute_conservation_laws=False,
+        )
+        with pytest.raises(RuntimeError, match="has already been imported"):
+            amici.import_model_module(
+                module_name=module_name, module_path=outdir
+            )
+        assert model_module_1.get_model().getParameters()[0] == 1.0

swig/modelname.template.i

@@ -9,6 +9,26 @@
 using namespace amici;
 %}
 
+// store the time a module was imported
+%{
+#include <ctime>
+static std::time_t _module_import_time;
+
+static std::time_t get_module_import_time() {
+    return _module_import_time;
+}
+
+static double get_import_time() {
+    return static_cast<double>(get_module_import_time());
+}
+%}
+
+static double get_import_time();
+
+%init %{
+    _module_import_time = std::time(nullptr);
+%}
+
 
 // Make model module accessible from the model
 %feature("pythonappend") amici::generic_model::getModel %{