fix kivy#3618 - add wraps decorator

Author: nrbrd

kivy/uix/sandbox.py

@@ -24,6 +24,7 @@
 
 __all__ = ('Sandbox', )
 
+from functools import wraps
 from kivy.context import Context
 from kivy.base import ExceptionManagerBase
 from kivy.clock import Clock
@@ -34,6 +35,7 @@
 
 
 def sandbox(f):
+    @wraps(f)
     def _f2(self, *args, **kwargs):
         ret = None
         with self: