implemented null object design pattern

pypatterns/behavioral/null.py

@@ -0,0 +1,75 @@
+class Null(object):
+    """
+    A class for implementing Null objects.
+
+    This class ignores all parameters passed when constructing or
+    calling instances and traps all attribute and method requests.
+    Instances of it always (and reliably) do 'nothing'.
+
+    The code might benefit from implementing some further special
+    Python methods depending on the context in which its instances
+    are used. Especially when comparing and coercing Null objects
+    the respective methods' implementation will depend very much
+    on the environment and, hence, these special methods are not
+    provided here.
+
+    Dinu C. Gherman,
+    August 2001
+    http://code.activestate.com/recipes/68205-null-object-design-pattern/
+    """
+
+    # object constructing
+
+    def __init__(self, *args, **kwargs):
+        """
+        Ignore parameters.
+        """
+        pass
+
+    # object calling
+
+    def __call__(self, *args, **kwargs):
+        """
+        Ignore method calls.
+        """
+        return self
+
+    # attribute handling
+
+    def __getattr__(self, mname):
+        """
+        Ignore attribute requests.
+        """
+        return self
+
+    def __setattr__(self, name, value):
+        """
+        Ignore attribute setting.
+        """
+        return self
+
+    def __delattr__(self, name):
+        """
+        Ignore deleting attributes.
+        """
+        return self
+
+    # misc.
+
+    def __repr__(self):
+        """
+        Return a string representation.
+        """
+        return ''
+
+    def __str__(self):
+        """
+        Convert to a string and return it.
+        """
+        return ''
+
+    def __bool__(self):
+        """
+        Boolean of Null object is always False.
+        """
+        return False