add Singleton pattern

Author: JakubVojvoda

singleton/Singleton.py

@@ -0,0 +1,41 @@
+#
+# Python Design Patterns: Singleton
+# Author: Jakub Vojvoda [github.com/JakubVojvoda]
+# 2016
+#
+# Source code is licensed under MIT License
+# (for more details see LICENSE)
+# 
+
+import sys
+
+#
+# Singleton
+# has variable to hold one instance of the class and 
+# method which gives us a way to instantiate the class
+#
+# reference: http://stackoverflow.com/questions/31875
+#
+class Singleton:
+  def __init__(self, instance):
+    self._instance = instance
+
+  def get(self):
+    try:
+      return self._only
+    except AttributeError:
+      self._only = self._instance()
+      return self._only
+
+  def __call__(self):
+    raise TypeError("...")
+
+@Singleton
+class Class:
+  def tell(self):
+    print("This is singleton.")
+ 
+
+if __name__ == "__main__": 
+  singleton = Class.get()
+  singleton.tell()