1. add a while True for sample

2. make the list of shards in cursor to a dict in internal code
3. test list 3-shard events in multiple times generate same results as
   list all events at once
4. Java is using sequential list, so it could give 1 shard cursor even
   there are 3 shards, the test makes sure python is working with 1 shard
   cursor.

sdk/storage/azure-storage-blob-changefeed/azure/storage/blob/changefeed/_change_feed_client.py

@@ -88,6 +88,7 @@ def list_changes(self, **kwargs):
 
         :keyword datetime start_time:
             Filters the results to return only events which happened after this time.
+            If start_time and continuation_token are both set, start_time will be ignored.
         :keyword datetime end_time:
             Filters the results to return only events which happened before this time.
         :keyword int results_per_page:

sdk/storage/azure-storage-blob-changefeed/azure/storage/blob/changefeed/_models.py

@@ -6,6 +6,7 @@
 # pylint: disable=too-few-public-methods, too-many-instance-attributes
 # pylint: disable=super-init-not-called, too-many-lines
 import collections
+import copy
 import json
 from datetime import datetime
 
@@ -50,13 +51,14 @@ def __init__(
             start_time=None,
             end_time=None,
             continuation_token=None):
-        if start_time and continuation_token:
-            raise ValueError("start_time and continuation_token shouldn't be specified at the same time")
         super(ChangeFeedPaged, self).__init__(
             get_next=self._get_next_cf,
             extract_data=self._extract_data_cb,
             continuation_token=continuation_token or ""
         )
+        # If start_time and continuation_token are both set, start_time will be ignored.
+        start_time = None if start_time and continuation_token else start_time
+
         continuation_token = eval(continuation_token) if continuation_token else None
 
         if continuation_token and container_client.primary_hostname != continuation_token['UrlHost']:
@@ -78,8 +80,13 @@ def _get_next_cf(self, continuation_token):  # pylint:disable=unused-argument
 
     def _extract_data_cb(self, event_list):
         self.current_page = event_list
-
-        return str(self._change_feed.cursor), self.current_page
+        try:
+            cursor = copy.deepcopy(self._change_feed.cursor)
+            shard_cursors = cursor['CurrentSegmentCursor']['ShardCursors']
+            cursor['CurrentSegmentCursor']['ShardCursors'] = [v for v in shard_cursors.values()]
+        except AttributeError:
+            pass
+        return str(cursor), self.current_page
 
 
 class ChangeFeed(object):
@@ -215,7 +222,7 @@ def __init__(self, client, segment_path, page_size, segment_cursor=None):
         self.segment_path = segment_path
         self.page_size = page_size
         self.shards = collections.deque()
-        self.cursor = {'ShardCursors': [], 'SegmentPath': self.segment_path}
+        self.cursor = {'ShardCursors': {}, 'SegmentPath': self.segment_path}
         self._initialize(segment_cursor=segment_cursor)
         # cursor is in this format {"segment_path", path, "CurrentShardPath": shard_path, "segment_cursor": ShardCursors dict}
 
@@ -234,14 +241,7 @@ def __next__(self):
                 pass
 
             # update cursor
-            is_shard_cursor_in_list = False
-            for shard_cursor in self.cursor['ShardCursors']:
-                if shard_cursor['CurrentChunkPath'] == shard.cursor['CurrentChunkPath']:
-                    shard_cursor['EventIndex'] = shard.cursor['EventIndex']
-                    shard_cursor['BlockOffset'] = shard.cursor['BlockOffset']
-                    is_shard_cursor_in_list = True
-            if not is_shard_cursor_in_list:
-                self.cursor['ShardCursors'].append(shard.cursor)
+            self.cursor['ShardCursors'][shard.shard_path] = shard.cursor
             self.cursor['CurrentShardPath'] = shard.shard_path
 
         if not segment_events:
@@ -268,11 +268,13 @@ def _initialize(self, segment_cursor=None):
                 self.shards.append(Shard(self.client, shard_path))
         else:
             start_shard_path = segment_cursor['CurrentShardPath']
+            shard_cursors = {shard_cursor['CurrentChunkPath'][:-10]: shard_cursor
+                             for shard_cursor in segment_cursor['ShardCursors']}
 
             if shard_paths:
-                # Initialize all shards using the shard cursors, skip those finished shards
-                for shard_cursor in segment_cursor['ShardCursors']:
-                    self.shards.append(Shard(self.client, shard_cursor['CurrentChunkPath'][:-10], shard_cursor))
+                # Initialize all shards using the shard cursors
+                for shard_path in shard_paths:
+                    self.shards.append(Shard(self.client, shard_path, shard_cursors.get(shard_path)))
 
                 # the move the shard behind start_shard_path one to the left most place, the left most shard is the next
                 # shard we should read based on continuation token.

sdk/storage/azure-storage-blob-changefeed/samples/change_feed_samples.py

@@ -98,37 +98,28 @@ def list_events_in_live_mode(self):
         # Instantiate a ChangeFeedClient
         cf_client = ChangeFeedClient("https://{}.blob.core.windows.net".format(self.ACCOUNT_NAME),
                                      credential=self.ACCOUNT_KEY)
-        # to get continuation token
-        start_time = datetime(2020, 8, 19, 10)
-        change_feed = cf_client.list_changes(start_time=start_time).by_page()
 
-        for page in change_feed:
-            for event in page:
-                print(event)
-        token = change_feed.continuation_token
+        start_time = datetime(2020, 9, 1, 1)
+        token = None
 
-        sleep(120)
-        print("continue printing events")
-        # restart using the continuation token
-        change_feed2 = cf_client.list_changes(results_per_page=56).by_page(continuation_token=token)
-        change_feed_page2 = next(change_feed2)
-        for event in change_feed_page2:
-            print(event)
+        while True:
+            # start_time will be ignored if start_time and continuation_token are both non-empty
+            change_feed = cf_client.list_changes(start_time=start_time).by_page(continuation_token=token)
 
-        sleep(120)
-        print("continue printing events")
+            for page in change_feed:
+                for event in page:
+                    print(event)
+            token = change_feed.continuation_token
 
-        token2 = change_feed2.continuation_token
-        change_feed3 = cf_client.list_changes(results_per_page=56).by_page(continuation_token=token2)
-        change_feed_page3 = next(change_feed3)
-        for event in change_feed_page3:
-            print(event)
+            sleep(60)
+            print("continue printing events")
 
 
 if __name__ == '__main__':
     sample = ChangeFeedSamples()
     sample.list_events_by_page()
     sample.list_all_events()
     sample.list_range_of_events()
-    sample.list_events_in_live_mode_continuously()
+    sample.list_events_using_continuation_token()
+    sample.list_events_in_live_mode()