Replaced some fatal errors with custom exceptions

conversion_utils/jos_msds_and_properties.py

@@ -230,6 +230,9 @@ class Msd:
         return isinstance(obj, Msd) and self.code == obj.code and self.language == obj.language
 
 
+class ConverterException(Exception):
+    pass
+
 class Converter:
     """Converter between Msd and Properties objects."""
 
@@ -254,7 +257,7 @@ class Converter:
         """Convert Msd to Properties (possibly in the other language)."""
  
         if (msd.code not in self.specifications.codes_map[msd.language]):
-            exit('[ERROR] msd {} is unknown'.format(msd.code))
+            raise ConverterException('The msd {} is unknown'.format(msd.code))
 
         category_char = msd.code[0].lower()
         value_chars = msd.code[1:]
@@ -270,8 +273,8 @@ class Converter:
                 feature_name = feature.names.get(language)
                 feature_value = value.names.get(language)
                 if (lemma is None and (category_name, index) in [(le[0], le[1]) for le in LEVEL_EXCEPTIONS]):
-                    exit('[ERROR] lemma is None but feature level depends on lemma for category={category}, position={position}'\
-                         .format(category=category_name, position=index))
+                    raise ConverterException('The lemma is None but feature level depends on lemma for category={category}, position={position}'\
+                                             .format(category=category_name, position=index))
                 level_exception_flag = (category_name, feature.position, lemma) in LEVEL_EXCEPTIONS
                 lexeme_level_flag = feature.lexeme_level_flag if not level_exception_flag else not feature.lexeme_level_flag
                 feature_value_list.append((feature, value))