[doc] improved assertion messages in trainer (#873)

colossalai/trainer/_trainer.py

-from typing import Union, List
-from colossalai.context.parallel_mode import ParallelMode
+from typing import Union, List, Any
 
 import torch
-from torch import Tensor
 from torch.utils.data import DataLoader
 from tqdm import tqdm
 
-from colossalai.core import global_context as gpc
-
 from colossalai.engine import Engine
 from colossalai.logging import DistributedLogger
 from colossalai.utils import MultiTimer
@@ -53,6 +49,7 @@ class Trainer:
     `Training with engine and trainer <https://www.colossalai.org/docs/basics/engine_trainer>`_
     and `ColossalAI-Examples <https://github.com/hpcaitech/ColossalAI-Examples/tree/main>`_.
     """
+
     def __init__(
         self,
         engine: Engine,
@@ -154,8 +151,7 @@ class Trainer:
     @staticmethod
     def _should_display_progress(display_progress: bool):
         """Only display progress on DP rank 0, TP rank 0 and PP last rank"""
-        return (display_progress and is_dp_rank_0() and is_tp_rank_0()
-                and is_no_pp_or_last_stage())
+        return (display_progress and is_dp_rank_0() and is_tp_rank_0() and is_no_pp_or_last_stage())
 
     def _train_epoch(
         self,
@@ -189,9 +185,7 @@ class Trainer:
                 return_output_label=return_output_label,
             )
             self.engine.step()
-            self._call_timer(action="stop",
-                             item="Train-step",
-                             keep_in_history=True)
+            self._call_timer(action="stop", item="Train-step", keep_in_history=True)
             self._call_hooks("after_train_iter", output=(logits, label, loss))
 
             self._cur_step += 1
@@ -204,9 +198,7 @@ class Trainer:
             if self._exceed_max_step():
                 break
 
-        self._call_timer(action="stop",
-                         item="Train-epoch",
-                         keep_in_history=True)
+        self._call_timer(action="stop", item="Train-epoch", keep_in_history=True)
         self._call_hooks("after_train_epoch")
         self._call_timer(action="reset", item="Train-epoch")
 
@@ -244,19 +236,14 @@ class Trainer:
                     return_loss=True,
                     return_output_label=return_output_label,
                 )
-                self._call_timer(action="stop",
-                                 item="Test-step",
-                                 keep_in_history=True)
-                self._call_hooks("after_test_iter",
-                                 output=(logits, label, loss))
+                self._call_timer(action="stop", item="Test-step", keep_in_history=True)
+                self._call_hooks("after_test_iter", output=(logits, label, loss))
 
                 if display_progress:
                     if "step_metrics" in self.states:
                         progress.set_postfix(**self.states["step_metrics"])
 
-        self._call_timer(action="stop",
-                         item="Test-epoch",
-                         keep_in_history=True)
+        self._call_timer(action="stop", item="Test-epoch", keep_in_history=True)
         self._call_hooks("after_test_epoch")
         self._call_hooks("after_test")
         self._call_timer(action="reset", item="Test-step")
@@ -303,9 +290,11 @@ class Trainer:
         # reset hooks
         self._reset_states()
         if hooks is not None:
-            assert isinstance(
-                hooks, list
-            ), f"expected argument hooks be to list, but got {type(hooks)}"
+            assert isinstance(hooks, list), f"expected argument hooks be to list, but got {type(hooks)}"
+
+            for hook in hooks:
+                assert isinstance(hook, BaseHook), \
+                    f'expected the hook to be of type BaseHook, but got {type(hook)}'
         else:
             hooks = []
         self.hooks = hooks
@@ -316,9 +305,7 @@ class Trainer:
                     f"Using {hook.__class__.__name__} for training, priority = {hook.priority}",
                     ranks=[0],
                 )
-            self._logger.info(
-                "Lower value means higher priority for calling hook function",
-                ranks=[0])
+            self._logger.info("Lower value means higher priority for calling hook function", ranks=[0])
         self._call_hooks("after_hook_is_attached")
 
         self._engine.train()
@@ -381,9 +368,7 @@ class Trainer:
         # reset hooks
         self._reset_states()
         if hooks is not None:
-            assert isinstance(
-                hooks, list
-            ), f"expected argument hooks be to list, but got {type(hooks)}"
+            assert isinstance(hooks, list), f"expected argument hooks be to list, but got {type(hooks)}"
         else:
             hooks = []
         self.hooks = hooks
@@ -394,9 +379,7 @@ class Trainer:
                     f"Using {hook.__class__.__name__} for training, priority = {hook.priority}",
                     ranks=[0],
                 )
-            self._logger.info(
-                "Lower value means higher priority for calling hook function",
-                ranks=[0])
+            self._logger.info("Lower value means higher priority for calling hook function", ranks=[0])
         self._call_hooks("after_hook_is_attached")
 
         # eval
@@ -406,7 +389,7 @@ class Trainer:
             return_output_label=return_output_label,
         )
 
-    def predict(self, data: Union[Tensor, List[Tensor]]):
+    def predict(self, data: Union[Any, List[Any]]):
         """Uses trained model to make a prediction for a tensor or a tensor list.
 
         Args:
@@ -416,17 +399,11 @@ class Trainer:
             :class:`torch.tensor`: The output of model as the prediction
         """
         # predict without labels
-        if isinstance(data, (list, tuple)):
-            assert isinstance(data[0], Tensor)
-        else:
-            assert isinstance(data, Tensor)
         self._engine.eval()
 
         # prepare a list of (data, label) to make it iterable
         # for compatibility with schedule
         simple_dataloader = [(data, None)]
         data_iter = iter(simple_dataloader)
-        output, _, _ = self.engine.execute_schedule(data_iter,
-                                                    forward_only=True,
-                                                    return_loss=False)
+        output, _, _ = self.engine.execute_schedule(data_iter, forward_only=True, return_loss=False)
         return output