fix train without eval bug

ppcls/engine/engine.py

@@ -116,7 +116,8 @@ class Engine(object):
         if self.mode == 'train':
             self.train_dataloader = build_dataloader(
                 self.config["DataLoader"], "Train", self.device, self.use_dali)
-        if self.mode in ["train", "eval"]:
+        if self.mode == "eval" or (self.mode == "train" and
+                                   self.config["Global"]["eval_during_train"]):
             if self.eval_mode == "classification":
                 self.eval_dataloader = build_dataloader(
                     self.config["DataLoader"], "Eval", self.device,
@@ -140,7 +141,8 @@ class Engine(object):
         if self.mode == "train":
             loss_info = self.config["Loss"]["Train"]
             self.train_loss_func = build_loss(loss_info)
-        if self.mode in ["train", "eval"]:
+        if self.mode == "eval" or (self.mode == "train" and
+                                   self.config["Global"]["eval_during_train"]):
             loss_config = self.config.get("Loss", None)
             if loss_config is not None:
                 loss_config = loss_config.get("Eval")
@@ -163,7 +165,8 @@ class Engine(object):
         else:
             self.train_metric_func = None
 
-        if self.mode in ["train", "eval"]:
+        if self.mode == "eval" or (self.mode == "train" and
+                                   self.config["Global"]["eval_during_train"]):
             metric_config = self.config.get("Metric")
             if self.eval_mode == "classification":
                 if metric_config is not None: