diff --git a/platypush/entities/_engine/__init__.py b/platypush/entities/_engine/__init__.py
index db071186d..19ead9727 100644
--- a/platypush/entities/_engine/__init__.py
+++ b/platypush/entities/_engine/__init__.py
@@ -4,7 +4,10 @@ from threading import Thread, Event
 from platypush.entities import Entity
 from platypush.utils import set_thread_name
 
+# pylint: disable=no-name-in-module
 from platypush.entities._engine.notifier import EntityNotifier
+
+# pylint: disable=no-name-in-module
 from platypush.entities._engine.queue import EntitiesQueue
 from platypush.entities._engine.repo import EntitiesRepository
 
@@ -18,7 +21,7 @@ class EntitiesEngine(Thread):
         1. Consume entities from a queue (synchronized with the upstream
            integrations that produce/handle them). The producer/consumer model
            ensure that only this thread writes to the database, packs events
-           together (preventing eccessive writes and throttling events), and
+           together (preventing excessive writes and throttling events), and
            prevents race conditions when SQLite is used.
         2. Merge any existing entities with their newer representations.
         3. Update the entities taxonomy.
@@ -66,7 +69,7 @@ class EntitiesEngine(Thread):
             try:
                 entities = self._repo.save(*entities)
             except Exception as e:
-                self.logger.error('Error while processing entity updates: ' + str(e))
+                self.logger.error('Error while processing entity updates: %s', e)
                 self.logger.exception(e)
                 continue
 
diff --git a/platypush/entities/_engine/notifier.py b/platypush/entities/_engine/notifier.py
index cc45fece2..92c32ec96 100644
--- a/platypush/entities/_engine/notifier.py
+++ b/platypush/entities/_engine/notifier.py
@@ -1,7 +1,9 @@
+from typing import Set, Tuple
 from platypush.context import get_bus
 from platypush.entities import Entity
 from platypush.message.event.entities import EntityUpdateEvent
 
+# pylint: disable=no-name-in-module
 from platypush.entities._engine.repo.cache import EntitiesCache
 
 
@@ -13,7 +15,7 @@ class EntityNotifier:
 
     def __init__(self, cache: EntitiesCache):
         self._cache = cache
-        self._entities_awaiting_flush = set()
+        self._entities_awaiting_flush: Set[Tuple[str, str]] = set()
 
     def _populate_entity_id_from_cache(self, new_entity: Entity):
         cached_entity = self._cache.get(new_entity)
diff --git a/platypush/entities/_engine/repo/__init__.py b/platypush/entities/_engine/repo/__init__.py
index ed355f341..73be43f70 100644
--- a/platypush/entities/_engine/repo/__init__.py
+++ b/platypush/entities/_engine/repo/__init__.py
@@ -4,7 +4,11 @@ from typing import Dict, Iterable, Tuple
 from sqlalchemy.orm import Session, make_transient
 
 from platypush.entities import Entity
+
+# pylint: disable=no-name-in-module
 from platypush.entities._engine.repo.cache import EntitiesCache
+
+# pylint: disable=no-name-in-module
 from platypush.entities._engine.repo.db import EntitiesDb
 from platypush.entities._engine.repo.merger import EntitiesMerger
 
diff --git a/platypush/entities/_engine/repo/cache.py b/platypush/entities/_engine/repo/cache.py
index 201714103..c38131a37 100644
--- a/platypush/entities/_engine/repo/cache.py
+++ b/platypush/entities/_engine/repo/cache.py
@@ -30,6 +30,8 @@ class EntitiesCache:
             if e:
                 return e
 
+        return None
+
     def update(self, *entities: Entity, overwrite=False):
         """
         Update the cache with a list of new entities.
diff --git a/platypush/entities/_engine/repo/db.py b/platypush/entities/_engine/repo/db.py
index 1114da34b..7dbc6a076 100644
--- a/platypush/entities/_engine/repo/db.py
+++ b/platypush/entities/_engine/repo/db.py
@@ -82,9 +82,15 @@ class EntitiesDb:
         rewired. Otherwise, we may end up with conflicts on entities that have
         already been flushed.
         """
-        # Index childrens by parent_id and by parent_key
-        children_by_parent_id = defaultdict(lambda: defaultdict(Entity))
-        children_by_parent_key = defaultdict(lambda: defaultdict(Entity))
+        # Index children by parent_id and by parent_key
+        children_by_parent_id: Dict[int, Dict[Tuple[str, str], Entity]] = defaultdict(
+            lambda: defaultdict(Entity)
+        )
+
+        children_by_parent_key: Dict[
+            Tuple[str, str], Dict[Tuple[str, str], Entity]
+        ] = defaultdict(lambda: defaultdict(Entity))
+
         for entity in entities:
             parent_key = None
             parent_id = entity.parent_id
@@ -113,8 +119,8 @@ class EntitiesDb:
             _TaxonomyAwareEntity(entity=e, level=0) for e in root_entities
         ]
 
-        batches = []
-        current_batch = []
+        batches: List[List[Entity]] = []
+        current_batch: List[_TaxonomyAwareEntity] = []
 
         while entities_to_process:
             # Pop the first element in the list (FIFO implementation)
diff --git a/platypush/entities/_engine/repo/merger.py b/platypush/entities/_engine/repo/merger.py
index b3b88dd45..a6bc3ea5d 100644
--- a/platypush/entities/_engine/repo/merger.py
+++ b/platypush/entities/_engine/repo/merger.py
@@ -12,9 +12,9 @@ class EntitiesMerger:
     """
 
     def __init__(self, repository):
-        from platypush.entities._engine.repo import EntitiesRepository
+        from . import EntitiesRepository
 
-        self._repo: EntitiesRepository = repository
+        self._repo: EntitiesRepository = repository  # type: ignore
 
     def merge(
         self,
@@ -26,8 +26,8 @@ class EntitiesMerger:
         the parent/child relationships and return a tuple with
         ``[new_entities, updated_entities]``.
         """
-        new_entities = {}
-        existing_entities = {}
+        new_entities: Dict[Tuple[str, str], Entity] = {}
+        existing_entities: Dict[Tuple[str, str], Entity] = {}
 
         self._merge(
             session,