Creational Design Pattern

app/data/__init__.py

@@ -5,9 +5,9 @@
 
 # Mapping of services to data-sources.
 DATA_SOURCES = {
-    "jhu": JhuLocationService(),
-    "csbs": CSBSLocationService(),
-    "nyt": NYTLocationService(),
+    "jhu": JhuLocationService.getInstance(),
+    "csbs": CSBSLocationService.getInstance(),
+    "nyt": NYTLocationService.getInstance(),
 }
 
 

app/services/location/csbs.py

@@ -20,6 +20,21 @@ class CSBSLocationService(LocationService):
     Service for retrieving locations from csbs
     """
 
+    __instance = None
+
+    @staticmethod
+    def getInstance():
+        if CSBSLocationService.__instance ==  None:
+            CSBSLocationService()
+        return CSBSLocationService.__instance
+
+    def __init__(self):
+        """ Virtually private constructor. """
+        if Singleton.__instance != None:
+            raise Exception("This class is a singleton!")
+        else:
+            Singleton.__instance = self
+
     async def get_all(self):
         # Get the locations.
         locations = await get_locations()

app/services/location/jhu.py

@@ -26,6 +26,21 @@ class JhuLocationService(LocationService):
     Service for retrieving locations from Johns Hopkins CSSE (https://github.com/CSSEGISandData/COVID-19).
     """
 
+    __instance = None
+
+    @staticmethod
+    def getInstance():
+        if CSBSLocationService.__instance ==  None:
+            CSBSLocationService()
+        return CSBSLocationService.__instance
+
+    def __init__(self):
+        """ Virtually private constructor. """
+        if Singleton.__instance != None:
+            raise Exception("This class is a singleton!")
+        else:
+            Singleton.__instance = self
+
     async def get_all(self):
         # Get the locations.
         locations = await get_locations()

app/services/location/nyt.py

@@ -21,6 +21,22 @@ class NYTLocationService(LocationService):
     Service for retrieving locations from New York Times (https://github.com/nytimes/covid-19-data).
     """
 
+
+    __instance = None
+
+    @staticmethod
+    def getInstance():
+        if CSBSLocationService.__instance ==  None:
+            CSBSLocationService()
+        return CSBSLocationService.__instance
+
+    def __init__(self):
+        """ Virtually private constructor. """
+        if Singleton.__instance != None:
+            raise Exception("This class is a singleton!")
+        else:
+            Singleton.__instance = self
+
     async def get_all(self):
         # Get the locations.
         locations = await get_locations()