Remove submodule, just put Dependencies in ./libs

libs/migrate/versioning/util/keyedinstance.py

@@ -0,0 +1,36 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+class KeyedInstance(object):
+    """A class whose instances have a unique identifier of some sort
+    No two instances with the same unique ID should exist - if we try to create
+    a second instance, the first should be returned. 
+    """
+
+    _instances = dict()
+
+    def __new__(cls, *p, **k):
+        instances = cls._instances
+        clskey = str(cls)
+        if clskey not in instances:
+            instances[clskey] = dict()
+        instances = instances[clskey]
+
+        key = cls._key(*p, **k)
+        if key not in instances:
+            instances[key] = super(KeyedInstance, cls).__new__(cls)
+        return instances[key]
+
+    @classmethod
+    def _key(cls, *p, **k):
+        """Given a unique identifier, return a dictionary key
+        This should be overridden by child classes, to specify which parameters 
+        should determine an object's uniqueness
+        """
+        raise NotImplementedError()
+
+    @classmethod
+    def clear(cls):
+        # Allow cls.clear() as well as uniqueInstance.clear(cls)
+        if str(cls) in cls._instances:
+            del cls._instances[str(cls)]