Merge pull request #40809 from geetachavan1/cherrypicks_NLYH0

[CherryPick:r2.3] Fix the api docstrings for `on_*_batch_begin` methods in `callbacks.Callback` class.

tensorflow/python/keras/callbacks.py

@@ -665,8 +665,9 @@ class Callback(object):
 
     Arguments:
         batch: Integer, index of batch within the current epoch.
-        logs: Dict. Has keys `batch` and `size` representing the current batch
-          number and the size of the batch.
+        logs: Dict, contains the return value of `model.train_step`. Typically,
+          the values of the `Model`'s metrics are returned.  Example:
+          `{'loss': 0.2, 'accuracy': 0.7}`.
     """
     # For backwards compatibility.
     self.on_batch_begin(batch, logs=logs)
@@ -697,8 +698,9 @@ class Callback(object):
 
     Arguments:
         batch: Integer, index of batch within the current epoch.
-        logs: Dict. Has keys `batch` and `size` representing the current batch
-          number and the size of the batch.
+        logs: Dict, contains the return value of `model.test_step`. Typically,
+          the values of the `Model`'s metrics are returned.  Example:
+          `{'loss': 0.2, 'accuracy': 0.7}`.
     """
 
   @doc_controls.for_subclass_implementers
@@ -725,8 +727,9 @@ class Callback(object):
 
     Arguments:
         batch: Integer, index of batch within the current epoch.
-        logs: Dict. Has keys `batch` and `size` representing the current batch
-          number and the size of the batch.
+        logs: Dict, contains the return value of `model.predict_step`,
+          it typically returns a dict with a key 'outputs' containing
+          the model's outputs.
     """
 
   @doc_controls.for_subclass_implementers