COW example...

1 files changed, 71 insertions, 0 deletions

diff --git a/lib/bb/COW.py b/lib/bb/COW.py
new file mode 100644
index 000000000..ac0e21c74
--- /dev/null
+++ b/lib/bb/COW.py
@@ -0,0 +1,71 @@
+# ex:ts=4:sw=4:sts=4:et
+# -*- tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*-
+"""
+This is a copy on write dictionary which abuses classes to be nice and fast.
+
+Please Note: Be careful when using mutable types (ie Dict and Lists). The copy on write stuff only kicks in on Assignment.
+"""
+
+from inspect import getmro
+
+class COWMeta(type):
+    def __str__(cls):
+        return "<COW Level: %i Current Keys: %i>" % (cls.__count__, len(cls.__dict__))
+    __repr__ = __str__
+
+    def cow(cls):
+        class C(cls):
+            __count__ = cls.__count__ + 1
+        return C
+
+    def __setitem__(cls, key, value):
+        setattr(cls, key, value)
+    def __getitem__(cls, key):
+        return getattr(cls, key)
+    def haskey(cls, key):
+        return hasattr(cls, key)
+
+    def iter(cls, type):
+        for key in dir(cls):
+            if key.startswith("__"):
+                continue
+
+            if type == "keys":
+                yield key
+            if type == "values":
+                yield cls[key]
+            if type == "items":
+                yield (key, cls[key])
+        raise StopIteration()
+
+    def iterkeys(cls):
+        return cls.iter("keys")
+    def itervalues(cls):
+        return cls.iter("values")
+    def iteritems(cls):
+        return cls.iter("items")
+    copy = cow
+
+class COWBase(object):
+    __metaclass__ = COWMeta
+    __count__ = 0
+
+if __name__ == "__main__":
+    a = COWBase
+    print a
+    a['a'] = 'a'
+    
+    b = a.copy()
+    print b
+    b['b'] = 'b'
+
+    for x in b.iteritems():
+        print x
+    print
+
+    b['a'] = 'c'
+
+    for x in b.iteritems():
+        print x
+    print
+