Update the docs of TaskManager (#586)

* Update manage.py

qlib/workflow/task/manage.py

@@ -47,6 +47,14 @@ class TaskManager:
     The tasks manager assumes that you will only update the tasks you fetched.
     The mongo fetch one and update will make it date updating secure.
 
+    This class can be used as a tool from commandline. Here are serveral examples
+
+    .. code-block:: shell
+
+        python -m qlib.workflow.task.manage -t <pool_name> wait
+        python -m qlib.workflow.task.manage -t <pool_name> task_stat
+
+
     .. note::
 
         Assumption: the data in MongoDB was encoded and the data out of MongoDB was decoded
@@ -80,7 +88,7 @@ def __init__(self, task_pool: str):
         task_pool: str
             the name of Collection in MongoDB
         """
-        self.task_pool = getattr(get_mongodb(), task_pool)
+        self.task_pool: pymongo.collection.Collection = getattr(get_mongodb(), task_pool)
         self.logger = get_module_logger(self.__class__.__name__)
 
     @staticmethod
@@ -101,6 +109,20 @@ def _encode_task(self, task):
         return task
 
     def _decode_task(self, task):
+        """
+        _decode_task is Serialization tool.
+        Mongodb needs JSON, so it needs to convert Python objects into JSON objects through pickle
+
+        Parameters
+        ----------
+        task : dict
+            task information
+
+        Returns
+        -------
+        dict
+            JSON required by mongodb
+        """
         for prefix in self.ENCODE_FIELDS_PREFIX:
             for k in list(task.keys()):
                 if k.startswith(prefix):
@@ -211,6 +233,7 @@ def create_task(self, task_def_l, dry_run=False, print_nt=False) -> List[str]:
                 r = self.task_pool.find_one({"filter": t})
             except InvalidDocument:
                 r = self.task_pool.find_one({"filter": self._dict_to_str(t)})
+            # When r is none, it indicates that r s a new task
             if r is None:
                 new_tasks.append(t)
                 if not dry_run:
@@ -461,11 +484,11 @@ def run_task(
 
     After running this method, here are 4 situations (before_status -> after_status):
 
-        STATUS_WAITING -> STATUS_DONE: use task["def"] as `task_func` param
+        STATUS_WAITING -> STATUS_DONE: use task["def"] as `task_func` param, it means that the task has not been started
 
         STATUS_WAITING -> STATUS_PART_DONE: use task["def"] as `task_func` param
 
-        STATUS_PART_DONE -> STATUS_PART_DONE: use task["res"] as `task_func` param
+        STATUS_PART_DONE -> STATUS_PART_DONE: use task["res"] as `task_func` param, it means that the task has been started but not completed
 
         STATUS_PART_DONE -> STATUS_DONE: use task["res"] as `task_func` param