Add fleet get_loss_scaling doc and update alert message (#32419)

python/paddle/distributed/fleet/base/fleet_base.py

@@ -1059,6 +1059,8 @@ class Fleet(object):
         return amp_optimizer
 
     def get_loss_scaling(self):
+        """Return the real-time loss scaling factor.
+        """
         amp_optimizer = self._get_amp_optimizer()
         return amp_optimizer.get_loss_scaling()
 

python/paddle/fluid/contrib/mixed_precision/decorator.py

@@ -98,7 +98,7 @@ class OptimizerWithMixedPrecision(object):
     def get_loss_scaling(self):
         """Return the real-time loss scaling factor.
         """
-        assert self._loss_scaling is not None, 'Call minimize() before calling get_loss_scaling()'
+        assert self._loss_scaling is not None, 'Please call minimize() before calling get_loss_scaling().'
         return self._loss_scaling
 
     def get_scaled_loss(self):