XoseLluis · July 6, 2022 15:46 · Jul 6, 2022
diff --git a/intercept_instance.py b/intercept_instance.py
@@ -0,0 +1,40 @@
+# In Groovy we can add interception to an instance (not to a whole class) by means of adding it to the instance metaclass
+# we can do something like that in Python by creating a new class that inherits the original class of the instance, and changing the class of the instance
+# in that new class we implement __getattribute__
+
+class Person:
+    def __init__(self, name):
+        self.name = name
+
+    def say_hi(self, person):
+        #print("inside say_hi")
+        return f"Hi person, I'm {self.name}"
+
+
+def add_interception_to_instance(obj, interceptor_fn):
+    class Interceptor_class(obj.__class__):
+        def __getattribute__(self, name):
+            interceptor_fn(self, name)
+            return object.__getattribute__(self, name)
+    obj.__class__ = Interceptor_class
+
+p1 = Person("Xuan")
+print(p1.say_hi("Francois"))
+# Hi person, I'm Xuan
+
+def logger_interceptor_fn(obj, attr):
+    print(f"intercepting access to {attr}")
+
+add_interception_to_instance(p1, logger_interceptor_fn)
+print(p1.say_hi("Francois"))
+#interception happens:
+# intercepting access to say_hi
+# intercepting access to name
+# Hi person, I'm Xuan
+print(isinstance(p1, Person))
+# True
+
+# other instances of Person are not intercepted
+p2 = Person("Iyan")
+print(p2.say_hi("Francois"))
+# Hi person, I'm Iyan