Fix newly reported pylint issues

Change-Id: Ie2fbd510ceefee844f3dbdbd6f4ce763beeb31da

cumin/__init__.py

@@ -100,13 +100,13 @@ def parse_config(config_file):
 
     """
     try:
-        with open(os.path.expanduser(config_file), 'r') as f:
+        with open(os.path.expanduser(config_file), 'r', encoding='utf8') as f:
             config = yaml.safe_load(f)
     except IOError as e:
-        raise CuminError('Unable to read configuration file: {message}'.format(message=e))
+        raise CuminError('Unable to read configuration file: {message}'.format(message=e)) from e
     except yaml.parser.ParserError as e:
         raise CuminError("Unable to parse configuration file '{config}':\n{message}".format(
-            config=config_file, message=e))
+            config=config_file, message=e)) from e
 
     if config is None:
         config = {}

cumin/backends/knownhosts.py

@@ -149,7 +149,7 @@ def _load_known_hosts(self):
 
         for filename in known_hosts_filenames:
             hosts = set()
-            with open(filename, 'r') as known_hosts_file:
+            with open(filename, 'r', encoding='utf8') as known_hosts_file:
                 for lineno, line in enumerate(known_hosts_file, 1):
                     try:
                         found, skipped = KnownHostsQuery.parse_known_hosts_line(line)

cumin/grammar.py

@@ -123,25 +123,25 @@ def _import_backend(module, available_backends):
         backend = importlib.import_module(module)
     except ImportError as e:
         if not module.startswith(INTERNAL_BACKEND_PREFIX):
-            raise CuminError("Unable to import backend '{module}': {e}".format(module=module, e=e))
+            raise CuminError("Unable to import backend '{module}': {e}".format(module=module, e=e)) from e
 
         return (None, None)  # Internal backend not available, are all the dependencies installed?
 
     name = module.split('.')[-1]
     message = "Unable to register backend '{name}' in module '{module}'".format(name=name, module=module)
     try:
         keyword = backend.GRAMMAR_PREFIX
-    except AttributeError:
-        raise CuminError('{message}: GRAMMAR_PREFIX module attribute not found'.format(message=message))
+    except AttributeError as e:
+        raise CuminError('{message}: GRAMMAR_PREFIX module attribute not found'.format(message=message)) from e
 
     if keyword in available_backends:
         raise CuminError(("{message}: keyword '{key}' already registered: {backends}").format(
             message=message, key=keyword, backends=available_backends))
 
     try:
         class_obj = backend.query_class
-    except AttributeError:
-        raise CuminError('{message}: query_class module attribute not found'.format(message=message))
+    except AttributeError as e:
+        raise CuminError('{message}: query_class module attribute not found'.format(message=message)) from e
 
     if not issubclass(class_obj, backends.BaseQuery):
         raise CuminError('{message}: query_class module attribute is not a subclass of cumin.backends.BaseQuery')

cumin/query.py

@@ -53,8 +53,9 @@ def execute(self, query_string):
             try:  # No default backend set, using directly the global grammar
                 return super().execute(query_string)
             except ParseException as e:
-                raise InvalidQueryError(("Unable to parse the query '{query}' with the global grammar and no "
-                                         "default backend is set:\n{error}").format(query=query_string, error=e))
+                raise InvalidQueryError(
+                    ("Unable to parse the query '{query}' with the global grammar and no "
+                     "default backend is set:\n{error}").format(query=query_string, error=e)) from e
 
         try:  # Default backend set, trying it first
             hosts = self._query_default_backend(query_string)
@@ -65,7 +66,8 @@ def execute(self, query_string):
                 raise InvalidQueryError(
                     ("Unable to parse the query '{query}' neither with the default backend '{name}' nor with the "
                      "global grammar:\n{name}: {e_def}\nglobal: {e_glob}").format(
-                        query=query_string, name=self.config['default_backend'], e_def=e_default, e_glob=e_global))
+                        query=query_string, name=self.config['default_backend'], e_def=e_default, e_glob=e_global)
+                ) from e_global
 
         return hosts
 

cumin/tests/__init__.py

@@ -15,7 +15,7 @@ def get_fixture(path, as_string=False):
         as_string: return the content as a multiline string instead of a list of lines [optional, default: False]
 
     """
-    with open(get_fixture_path(path)) as f:
+    with open(get_fixture_path(path), encoding='utf8') as f:
         if as_string:
             content = f.read()
         else: