Add more assertions in KafkaConsumer (primarily to seek* methods)

kafka/consumer/group.py

@@ -461,9 +461,11 @@ class KafkaConsumer(six.Iterator):
 
         Arguments:
             partition (TopicPartition): partition to check
-        """
-        assert self._subscription.is_assigned(partition)
 
+        Returns:
+            int: offset
+        """
+        assert self._subscription.is_assigned(partition), 'Partition is not assigned'
         offset = self._subscription.assignment[partition].position
         if offset is None:
             self._update_fetch_positions(partition)
@@ -529,8 +531,13 @@ class KafkaConsumer(six.Iterator):
         Arguments:
             partition (TopicPartition): partition for seek operation
             offset (int): message offset in partition
+
+        Raises:
+            AssertionError: if offset is not an int >= 0; or if partition is not
+                currently assigned.
         """
-        assert offset >= 0
+        assert isinstance(offset, int) and offset >= 0, 'Offset must be >= 0'
+        assert partition in self._subscription.assigned_partitions(), 'Unassigned partition'
         log.debug("Seeking to offset %s for partition %s", offset, partition)
         self._subscription.assignment[partition].seek(offset)
 
@@ -540,9 +547,18 @@ class KafkaConsumer(six.Iterator):
         Arguments:
             *partitions: optionally provide specific TopicPartitions, otherwise
                 default to all assigned partitions
+
+        Raises:
+            AssertionError: if any partition is not currently assigned, or if
+                no partitions are assigned
         """
         if not partitions:
             partitions = self._subscription.assigned_partitions()
+            assert partitions, 'No partitions are currently assigned'
+        else:
+            for p in partitions:
+                assert p in self._subscription.assigned_partitions(), 'Unassigned partition'
+
         for tp in partitions:
             log.debug("Seeking to beginning of partition %s", tp)
             self._subscription.need_offset_reset(tp, OffsetResetStrategy.EARLIEST)
@@ -553,9 +569,18 @@ class KafkaConsumer(six.Iterator):
         Arguments:
             *partitions: optionally provide specific TopicPartitions, otherwise
                 default to all assigned partitions
+
+        Raises:
+            AssertionError: if any partition is not currently assigned, or if
+                no partitions are assigned
         """
         if not partitions:
             partitions = self._subscription.assigned_partitions()
+            assert partitions, 'No partitions are currently assigned'
+        else:
+            for p in partitions:
+                assert p in self._subscription.assigned_partitions(), 'Unassigned partition'
+
         for tp in partitions:
             log.debug("Seeking to end of partition %s", tp)
             self._subscription.need_offset_reset(tp, OffsetResetStrategy.LATEST)