[utils] Add frozen class decorator

This decorator disable the possibility to add attributes to
to python objects outside the __init__ function.

beat/editor/utils.py

@@ -31,10 +31,11 @@ Helper methods and utilities
 
 import os
 import sys
+import logging
 
 import jinja2
 
-import logging
+from functools import wraps
 
 logger = logging.getLogger(__name__)
 
@@ -217,3 +218,37 @@ def setup_logger(name, verbosity):
         logger.setLevel(logging.DEBUG)
 
     return logger
+
+
+def frozen(cls):
+    """
+    Don't allow new attributes to be added outside of init
+
+    Based on https://stackoverflow.com/a/29368642/5843716
+    """
+    cls.__frozen = False
+
+    def frozensetattr(self, key, value):
+        """Don't allow attributes to be added outside of __init__"""
+
+        if self.__frozen and not hasattr(self, key):
+            print(
+                "Class {} is frozen. Cannot set {} = {}".format(
+                    cls.__name__, key, value
+                )
+            )
+        else:
+            object.__setattr__(self, key, value)
+
+    def init_decorator(func):
+        @wraps(func)
+        def wrapper(self, *args, **kwargs):
+            func(self, *args, **kwargs)
+            self.__frozen = True
+
+        return wrapper
+
+    cls.__setattr__ = frozensetattr
+    cls.__init__ = init_decorator(cls.__init__)
+
+    return cls