add new private decorator

src/aura_engine/base/lang.py

+#
+# Aura Engine (https://gitlab.servus.at/aura/engine)
+#
+# Copyright (C) 2017-2020 - The Aura Engine Team.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+"""
+A collection of Python language utilities.
+"""
+
+import inspect
+from functools import wraps
+
+
+def private(member):
+    """
+    @private Decorator.
+
+    Use this to annotate your methods for private-visibility.
+
+    This is an more expressive alternative to the pythonic underscore visibility.
+    """
+
+    @wraps(member)
+    def wrapper(*args):
+        me = member.__name__
+        stack = inspect.stack()
+        calling_class = stack[1][0].f_locals["self"].__class__.__name__
+        calling_method = stack[1][0].f_code.co_name
+        if calling_method not in dir(args[0]) and calling_method is not me:
+            msg = f'"{me}(..)" called by "{calling_class}.{calling_method}(..)" is private'
+            print(msg)
+            raise Exception(msg)
+        return member(*args)
+
+    return wrapper