add loss container

engine/util/container.py

@@ -0,0 +1,9 @@
+class LossContainer:
+    def __init__(self, weight, loss):
+        self.weight = weight
+        self.loss = loss
+
+    def __call__(self, *args, **kwargs):
+        if self.weight > 0:
+            return self.weight * self.loss(*args, **kwargs)
+        return 0.0