Introduce validator metaclass

rest_framework/class_validator.py

@@ -0,0 +1,41 @@
+"""Attribute checking for Python classes
+"""
+
+class InvalidAttributeError(AttributeError):
+    """
+    Use this for invalid attributes because AttributeError means not found
+    """
+
+    pass
+
+
+class ValidatorMeta(type):
+    """
+    Metaclass to guard against setting unrecognized attributes
+    Set it as __metaclass__ as low in the inheritance chain as possible
+    """
+    def __new__(cls, name, parents, kwargs):
+        """Creates the new class, and sees if it has only known attributes
+        """
+        new_cls = type.__new__(cls, name, parents, kwargs)
+
+        ## Fail only if the new class defines an api
+        if not new_cls.__dict__.has_key('valid_attributes'):
+            return new_cls
+
+        ## Do some sanity checks to not fail in vain
+        for attr, val in kwargs.items():
+            if attr == 'valid_attributes':
+                continue
+            if attr.startswith('_'):
+                continue
+            # Methods are always allowed
+            if callable(val):
+                continue
+
+            # Ensure validity
+            if not attr in new_cls.valid_attributes:
+                raise InvalidAttributeError(attr)
+
+        return new_cls
+