bug fix

python/paddle/fluid/trainer.py

@@ -139,11 +139,12 @@ class Trainer(object):
         self.trainer_id = 0
         self.chief = True
         self.checkpoint = checkpoint_config
-        if self.checkpoint and \
-            not isinstance(self.checkpoint, CheckpointConfig):
+        if self.checkpoint:
+            if not isinstance(self.checkpoint, CheckpointConfig):
                 raise TypeError(
                     "The checkpoint_config shoule be an instance of CheckpointConfig"
                 )
+            else:
                 self.checkpoint._load_serial = io.need_load_checkpoint(
                     self.checkpoint.checkpoint_dir)
 
@@ -175,7 +176,7 @@ class Trainer(object):
             exe = executor.Executor(place)
             exe.run(self.startup_program)
 
-        if self.checkpoint._load_serial:
+        if self.checkpoint and self.checkpoint._load_serial:
             exe = executor.Executor(place)
             io.load_checkpoint(exe, self.checkpoint.checkpoint_dir,
                                self.checkpoint._load_serial,