diff --git a/src/dynamic_graph/signal_base.py b/src/dynamic_graph/signal_base.py
index 034b041dfafe9de73eb5ab293f385d4d079f97c9..0e0ce5ede3bd55ba10e27cf6f77d6e568a46b01d 100644
--- a/src/dynamic_graph/signal_base.py
+++ b/src/dynamic_graph/signal_base.py
@@ -101,12 +101,12 @@ def objectToString(obj) :
       - an integer,
       - a boolean,
     """
-    if (isinstance(obj, collections.Iterable)) :
+    if (hasattr (obj, "__iter__")) :
         # matrix or vector
         if len(obj) is 0 :
             return ""
         else :
-            if (isinstance(obj[0], collections.Iterable)) :
+            if (hasattr(obj[0], "__iter__")) :
                 #matrix
                 return matrixToString(obj)
             else :