avoid adding the append callback twice if the same source is added twice

kabuki/cacher.py

@@ -7,28 +7,26 @@ class Cacher:
     def __init__(self):
         self.caches = {}
 
+
     def add_source(self, src, size=100):
         name = src.name
         if not src.is_connected:
             raise RuntimeError(f"source NOT connected: {name}")
-        cache = self.add_cache(name, size=size)
-        src.add_callback(cache.callback_append)
-        return cache
 
-    def add_cache(self, name, size=100):
-        # key contains size in case multiple caches per name with different sizes are needed
-        key = (name, size)
         caches = self.caches
         try:
-            return caches[key]
+            return caches[name]
         except KeyError:
-            caches[key] = cache = Cache(size=size)
+            caches[name] = cache = Cache(size=size)
+            src.add_callback(cache.callback_append)
             return cache
 
+
     def __repr__(self):
         return repr(self.caches)
 
 
+
 class Cache:
 
     def __init__(self, size=100):