renaming method name

teacher_base.py

@@ -36,7 +36,7 @@ class TeacherBase(abc.ABC):
         pass
 
     @abc.abstractmethod
-    def is_positive_example(self, ex) -> Optional[bool]:
+    def is_safe_state(self, ex) -> Optional[bool]:
         raise NotImplementedError
 
     @abc.abstractmethod