Simplify _linear_model_fn

* reduce line count using getattr() on layers 'weighted_sum...' rather than two explicit calls

*  create a variable that has a reference to the correct function

as suggested

* use a better name for the logit function

* use regular if statement

* be more explicit in if statement

* fix whitespace

* whitespace fix

Author: ariejdl

tensorflow/contrib/learn/python/learn/estimators/linear.py

@@ -149,21 +149,16 @@ def _linear_model_fn(features, labels, mode, params, config=None):
       values=tuple(six.itervalues(features)),
       partitioner=partitioner) as scope:
     if joint_weights:
-      logits, _, _ = (
-          layers.joint_weighted_sum_from_feature_columns(
-              columns_to_tensors=features,
-              feature_columns=feature_columns,
-              num_outputs=head.logits_dimension,
-              weight_collections=[parent_scope],
-              scope=scope))
+      layer_fn = layers.joint_weighted_sum_from_feature_columns
     else:
-      logits, _, _ = (
-          layers.weighted_sum_from_feature_columns(
-              columns_to_tensors=features,
-              feature_columns=feature_columns,
-              num_outputs=head.logits_dimension,
-              weight_collections=[parent_scope],
-              scope=scope))
+      layer_fn = layers.weighted_sum_from_feature_columns
+        
+    logits, _, _ = layer_fn(
+            columns_to_tensors=features,
+            feature_columns=feature_columns,
+            num_outputs=head.logits_dimension,
+            weight_collections=[parent_scope],
+            scope=scope)
 
     def _train_op_fn(loss):
       global_step = contrib_variables.get_global_step()