added utils.py with Singleton metaclass

db/create.py

@@ -13,7 +13,7 @@ Create database file and tables if not exists.
     |by_request    |                 +---------------+
     +--------------+
 
-* services table
+* **services table**
     * **service_id:**      service id
                                *(integer primary key)*.
     * **token:**           service token for access to api
@@ -26,7 +26,7 @@ Create database file and tables if not exists.
                                *(integer with 0 as default)*.
     * **by_request:**      send notifications automatically or not
                                *(integer with 0 as default)*.
-* notifications table
+* **notifications table**
     * **notification_id:** notification id
                                *(integer primary key)*.
     * **service_id:**      service id
@@ -73,4 +73,5 @@ def create_tables_if_not_exists(dbfile: str) -> None:
     cursor.execute(CREATE_SERVICES_TABLE)
     cursor.execute(CREATE_NOTIFICATIONS_TABLE)
     connection.commit()
+    cursor.close()
     connection.close()

utils.py

@@ -0,0 +1,8 @@
+class Singleton(type):
+    """Singleton metaclass"""
+    _instances = {}
+
+    def __call__(cls, *args, **kwargs):
+        if cls not in cls._instances:
+            cls._instances[cls] = super().__call__(*args, **kwargs)
+        return cls._instances[cls]