[EN-1570] handler docstrings

Author: iamishalkin

docs/api.rst

@@ -14,6 +14,10 @@ API
 	:members:
 	:inherited-members:
 
+.. automodule:: dxfeed.core.utils.handler
+	:members:
+	:inherited-members:
+
 Low-level API
 -----------------------
 
@@ -28,5 +32,3 @@ Utils functions
 	:members:
 	:inherited-members:
 
-.. automodule:: dxfeed.core.utils.data_class
-	:members:

dxfeed/core/utils/handler.pyx

@@ -4,31 +4,94 @@ import pandas as pd
 
 
 cdef class EventHandler:
-    # TODO: docs
+    """
+    Master class for user defined event handlers. `update` method should be considered as abstract.
+
+    Attributes
+    ----------
+    columns: list
+        After attaching listener the field contains one-word descriptors of the values in upcoming event the order
+        coincides
+    """
     def __init__(self):
         self.columns = list()
 
     cdef void __update(self, event) nogil:
         with gil:
             self.update(event)
 
-    def update(self, event):
+    def update(self, event: list):
+        """
+        Method that is called, when event arrives to related Subscription. Currently (Cython version 0.29.17),
+        abstract methods are not implemented, so this implementation is sort of stub method.
+
+        Parameters
+        ----------
+        event: list
+            List of various data specific to certain event type
+        """
         warn(Warning('You have not implemented update method in your EventHandler, that is called, when event comes!'))
 
 cdef class DefaultHandler(EventHandler):
-    # TODO: docs
+    """
+    The class implements one possible event handler, which is considered as default. This class just stores upcoming
+    events in deque and has methods to get data as list or as pandas.DataFrame.
+
+    Attributes
+    ----------
+    data_len: int
+        The length of internal collections.deque object. Default is 100000.
+    columns: list
+        After attaching listener the field contains one-word descriptors of the values in upcoming event the order
+        coincides.
+    """
     def __init__(self, data_len: int=100000):
         self.__data = deque(maxlen=data_len)
 
-    def update(self, event):
+    def update(self, event: list):
+        """
+        Utility method that is called by underlying Cython level when new event is received. Sores events in
+        collection.deque.
+
+        Parameters
+        ----------
+        event: list
+            List of various data specific to certain event type.
+        """
         self.__data.append(event)
 
     def get_list(self):
+        """
+        Method to get data stored in collections.deque as list.
+
+        Returns
+        -------
+        data: list
+            List of received events.
+        """
         data = self.__data.copy()
         self.__data.clear()
         return list(data)
 
     def get_dataframe(self, keep: bool=True):
+        """
+        Returns received data as pandas.DataFrame object.
+
+        Warning
+        -------
+        There are no restriction on attaching one event handler to several subscriptions. In this case, method will
+        work correctly if different subscriptions have same event type. Otherwise error will occur.
+
+        Parameters
+        ----------
+        keep: bool
+            When False clears internal collections.deque object after call. Default True.
+
+        Returns
+        -------
+        df: pandas.DataFrame
+            Dataframe with received events.
+        """
         df_data = self.__data.copy()
         if not keep:
             self.__data.clear()