#15

satella/coding/singleton.py

 # coding=UTF-8
 from __future__ import print_function, absolute_import, division
 import functools
+import six
 
 
-def Singleton(cls):
-    """
-    Make a singleton out of decorated class.
+if six.PY3:
 
-    Taken from https://wiki.python.org/moin/PythonDecoratorLibrary
+    # Taken from https://wiki.python.org/moin/PythonDecoratorLibrary
+    def Singleton(cls):
+        """
+        Make a singleton out of decorated class.
 
-    Usage:
+        Usage:
 
-        @Singleton
-        class MyClass(object):
-            ...
-    """
+            @Singleton
+            class MyClass(object):
+                ...
+        """
 
-    cls.__new_old__ = cls.__new__
+        cls.__new_old__ = cls.__new__
 
-    @functools.wraps(cls.__new__)
-    def singleton_new(cls, *args, **kw):
-        it =  cls.__dict__.get('__it__')
-        if it is not None:
-            return it
-
-        cls.__it__ = it = cls.__new_old__(cls, *args, **kw)
-        it.__init_old__(*args, **kw)
-        return it
+        @functools.wraps(cls.__new__)
+        def singleton_new(cls, *args, **kw):
+            it =  cls.__dict__.get('__it__')
+            if it is not None:
+                return it
 
-    cls.__new__ = singleton_new
-    cls.__init_old__ = cls.__init__
-    cls.__init__ = object.__init__
+            cls.__it__ = it = cls.__new_old__(cls, *args, **kw)
+            it.__init_old__(*args, **kw)
+            return it
 
-    return cls
+        cls.__new__ = singleton_new
+        cls.__init_old__ = cls.__init__
+        cls.__init__ = object.__init__
+
+        return cls
+else:
+    class _SingletonWrapper:
+        """
+        A singleton wrapper class. Its instances would be created
+        for each decorated class.
+        """
+
+        def __init__(self, cls):
+            self.__wrapped__ = cls
+            self._instance = None
+
+        def __call__(self, *args, **kwargs):
+            """Returns a single instance of decorated class"""
+            if self._instance is None:
+                self._instance = self.__wrapped__(*args, **kwargs)
+            return self._instance
+
+    # taken from https://pypi.python.org/pypi/singleton-decorator/1.0.0
+    def Singleton(cls):
+        """
+        A singleton decorator. Returns a wrapper objects. A call on that object
+        returns a single instance object of decorated class. Use the __wrapped__
+        attribute to access decorated class directly in unit tests.
+        """
+        return _SingletonWrapper(cls)