pyosys: catch boost::python::error_already_set

* This catches exceptions from internal passes, printing them in a
  readable manner where the user would otherwise see an unspecified
  boost exception

kernel/driver.cc

@@ -55,6 +55,10 @@
 #  include <unistd.h>
 #endif
 
+#ifdef WITH_PYTHON
+#  include <boost/python.hpp>
+#endif
+
 USING_YOSYS_NAMESPACE
 
 #ifdef EMSCRIPTEN
@@ -525,6 +529,11 @@ int main(int argc, char **argv)
 			run_shell = false;
 	}
 
+#ifdef WITH_PYTHON
+	// For boost::python::error_already_set
+	try {
+#endif
+
 	if (!topmodule.empty())
 		run_pass("hierarchy -top " + topmodule);
 	if (!scriptfile.empty()) {
@@ -596,6 +605,13 @@ int main(int argc, char **argv)
 			run_backend(output_filename, backend_command);
 	}
 
+#ifdef WITH_PYTHON
+	} catch (boost::python::error_already_set &) {
+		PyErr_Print();
+		log_error("Python interpreter encountered an exception.\n");
+	}
+#endif
+
 	yosys_design->check();
 	for (auto it : saved_designs)
 		it.second->check();