patch made from https://github.com/benoitc/socketpool/blob/06d659612f15cb4c207a2fc508b6099e09d3fde7/socketpool/pool.py
in reply to;  size is supposed to be a property. fix #20
commit 06d659612f15cb4c207a2fc508b6099e09d3fde7.
file included changes making the first hunk
diff -ur socketpool-0.5.2.orig/socketpool/pool.py socketpool-0.5.2/socketpool/pool.py
--- socketpool/pool.py	2012-08-05 12:22:13.000000000 +0800
+++ socketpool/pool.py	2013-02-10 22:51:45.607637365 +0800
@@ -48,8 +48,12 @@
                  max_size=10, options=None,
                  reap_connections=True, backend="thread"):
 
-        self.backend_mod = load_backend(backend)
-        self.backend = backend
+        if isinstance(backend, str):
+            self.backend_mod = load_backend(backend)
+            self.backend = backend
+        else:
+            self.backend_mod = backend
+            self.backend = str(getattr(backend, '__name__', backend))
         self.max_size = max_size
         self.pool = getattr(self.backend_mod, 'PriorityQueue')()
         self._free_conns = 0
@@ -97,6 +101,7 @@
         if conn.is_connected():
             conn.invalidate()
 
+    @property
     def size(self):
         return self.pool.qsize()
 
@@ -193,3 +198,4 @@
         finally:
             self.release_connection(conn)
 
+