#23 - python

Author: duendeintemporal

Roadmap/23 - SINGLETON/python/duendeintemporal.py

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+#23 { Retos para Programadores } PATRONES DE DISEÑO: SINGLETON
+
+# Bibliography reference
+# I use GPT as a reference and sometimes to correct or generate proper comments.
+
+"""  
+ * EJERCICIO:
+ * Explora el patrón de diseño "singleton" y muestra cómo crearlo
+ * con un ejemplo genérico.
+ *
+ * DIFICULTAD EXTRA (opcional):
+ * Utiliza el patrón de diseño "singleton" para representar una clase que
+ * haga referencia a la sesión de usuario de una aplicación ficticia.
+ * La sesión debe permitir asignar un usuario (id, username, nombre y email),
+ * recuperar los datos del usuario y borrar los datos de la sesión.
+
+"""
+
+log = print
+log('Retos para Programadores #23')
+
+# The Singleton design pattern ensures that a class has a single instance
+# and provides a global point of access to that instance. Below, I will show
+# you how to implement the Singleton pattern in Python, followed by an example
+# that represents a class for managing user sessions.
+
+# Implementation of the Singleton Pattern
+
+class Singleton:
+    _instance = None  # Class variable to hold the single instance
+
+    def __new__(cls):
+        if cls._instance is None:
+            cls._instance = super(Singleton, cls).__new__(cls)
+            # Initialize any properties you need here
+        return cls._instance
+
+    # Example method
+    def some_method(self):
+        print("This is a method of the singleton.")
+
+# Using the Singleton
+instance1 = Singleton()
+instance2 = Singleton()
+
+# Note: both variables point to the same instance
+log(instance1.some_method()) # This is a method of the singleton.
+log(instance1 is instance2)  # True
+
+# EXTRA DIFFICULTY EXERCISE
+
+class UserSession:
+    _instance = None  # Class variable to hold the single instance
+
+    def __new__(cls):
+        if cls._instance is None:
+            cls._instance = super(UserSession, cls).__new__(cls)
+            cls._instance.user = None  # Initialize user property
+        return cls._instance
+
+    def set_user(self, id, username, name, email):
+        self.user = {'id': id, 'username': username, 'name': name, 'email': email}
+
+    def get_user(self):
+        return self.user
+
+    def clear_session(self):
+        self.user = None
+
+# Example usage of UserSession
+session1 = UserSession()
+session1.set_user(1, 'FritzCat', 'Fritz Cat', '[email protected]')
+
+log(session1.get_user())  # {'id': 1, 'username': 'FritzCat', 'name': 'Fritz Cat', 'email': '[email protected]'}
+
+session2 = UserSession()
+log(session2.get_user())  # {'id': 1, 'username': 'FritzCat', 'name': 'Fritz Cat', 'email': '[email protected]'}
+
+session2.clear_session()
+log(session1.get_user())  
+    
+    # Note: 
+"""  
+When you call session2.clear_session(), it sets the user attribute to None. Since both session1 and session2 refer to the same instance, calling session1.get_user() afterward will also return None.
+
+"""
+