Allow Delegator to delete Python rates

include/cantera/base/Delegator.h

@@ -9,6 +9,7 @@
 #include "cantera/base/global.h"
 #include "cantera/base/ctexceptions.h"
 #include <array>
+#include <list>
 
 namespace Cantera
 {
@@ -100,6 +101,12 @@ namespace Cantera
 class Delegator
 {
 public:
+    ~Delegator() {
+        for (auto& func : m_cleanup_funcs) {
+            func();
+        }
+    }
+
     //! Set delegates for member functions with the signature `void()`.
     void setDelegate(const std::string& name, const std::function<void()>& func,
                      const std::string& when)
@@ -227,6 +234,10 @@ class Delegator
         *m_funcs_sz_csr[name] = makeDelegate(func, when, m_base_sz_csr[name]);
     }
 
+    void addCleanupFunc(const std::function<void()>& func) {
+        m_cleanup_funcs.push_back(func);
+    }
+
 protected:
     //! Install a function with the signature `void()` as being delegatable
     void install(const std::string& name, std::function<void()>& target,
@@ -446,6 +457,9 @@ class Delegator
     std::map<std::string,
         std::function<size_t(const std::string&)>*> m_funcs_sz_csr;
     //! @}
+
+    //! Cleanup functions to be called from the destructor
+    std::list<std::function<void()>> m_cleanup_funcs;
 };
 
 }

src/extensions/PythonExtensionManager.cpp

@@ -72,14 +72,25 @@ void PythonExtensionManager::registerRateBuilders(const string& extensionName)
                          "Got unparsable input from ct_getPythonExtensibleRateTypes:"
                          "\n'''{}\n'''", rateTypes);
         }
+
         string rateName = tokens[0];
 
         // Create a function that constructs and links a C++ ReactionRateDelegator
         // object and a Python ExtensibleRate object of a particular type, and register
         // this as the builder for reactions of this type
         auto builder = [rateName, extensionName](const AnyMap& params, const UnitStack& units) {
             auto delegator = make_unique<ReactionRateDelegator>();
-            ct_addPythonExtensibleRate(delegator.get(), extensionName, rateName);
+            PyObject* extRate = ct_newPythonExtensibleRate(delegator.get(),
+                    extensionName, rateName);
+            if (extRate == nullptr) {
+                throw CanteraError("PythonExtensionManager::registerRateBuilders",
+                                   "ct_newPythonExtensibleRate failed");
+            }
+
+            // Make the delegator responsible for eventually deleting the Python object
+            Py_IncRef(extRate);
+            delegator->addCleanupFunc([extRate]() { Py_DecRef(extRate); });
+
             return delegator.release();
         };
         ReactionRateFactory::factory()->reg(tokens[1], builder);

src/extensions/pythonExtensions.pyx

@@ -40,13 +40,12 @@ cdef public char* ct_getPythonExtensibleRateTypes(const string& module_name) exc
     return c_string
 
 
-cdef public int ct_addPythonExtensibleRate(CxxReactionRateDelegator* delegator,
-                                            const string& module_name,
-                                            const string& class_name) except -1:
+cdef public object ct_newPythonExtensibleRate(CxxReactionRateDelegator* delegator,
+                                              const string& module_name,
+                                              const string& class_name):
 
     mod = importlib.import_module(module_name.decode())
     cdef ExtensibleRate rate = getattr(mod, class_name.decode())(init=False)
-    Py_INCREF(rate)
     rate.set_cxx_object(delegator)
     assign_delegates(rate, delegator)
-    return 0
+    return rate