Add error handler for python exceptions

typon/trans/transpiler/phases/emit_cpp/module.py

@@ -60,6 +60,7 @@ class ModuleVisitor(BlockVisitor):
 
         yield ") {"
         yield "InterpGuard guard{};"
+        yield "try {"
         yield f"return py::module_::import(\"{mod}\").attr(\"{name}\")("
         for i, argty in enumerate(fty.parameters):
             if i != 0:
@@ -68,6 +69,10 @@ class ModuleVisitor(BlockVisitor):
         yield ").cast<"
         yield from self.visit(fty.return_type)
         yield ">();"
+        yield "} catch (py::error_already_set& e) {"
+        yield 'std::cerr << "Python exception: " << e.what() << std::endl;'
+        yield "throw;"
+        yield "}"
         yield "}"
         yield f"}} {alias};"