add basic validation support

api/validators.py

@@ -0,0 +1,14 @@
+# coding=UTF-8
+
+class ValidationError(Exception):
+
+    def __init__(self, message):
+        Exception.__init__(self)
+        self.message = message
+
+
+def validate_keys_exists(obj, *keys):
+    for key in keys:
+        if not key in obj:
+            raise ValidationError('No {} is specified'.format(key))
+    return True