user need to set feed order for Trainer.train and Trainer.test (#10679)

Author: jacquesqiao

python/paddle/fluid/trainer.py

@@ -172,9 +172,9 @@ def _dist_transpile_if_necessary(self, optimize_ops, params_grads):
     def train(self,
               num_epochs,
               event_handler,
-              reader=None,
-              parallel=False,
-              feed_order=None):
+              reader,
+              feed_order,
+              parallel=False):
         """
         Train the model.
 
@@ -202,7 +202,7 @@ def train(self,
 
         self._train_by_executor(num_epochs, event_handler, reader, feed_order)
 
-    def test(self, reader, feed_order=None):
+    def test(self, reader, feed_order):
         """
         Test the model on given test data
 
@@ -276,12 +276,7 @@ def build_feed_var_list(program, feed_order):
     if not isinstance(program, framework.Program):
         raise TypeError("The 'program' should be an object of Program")
 
-    if feed_order is None:
-        feed_var_list = [
-            var for var in program.global_block().vars.itervalues()
-            if var.is_data
-        ]
-    elif isinstance(feed_order, list):
+    if isinstance(feed_order, list):
         feed_var_list = [
             program.global_block().var(var_name) for var_name in feed_order
         ]