clearer Elemwise/Scalar __str__.

theano/scalar/basic.py

@@ -869,7 +869,8 @@ class ScalarOp(Op):
             return self.name
         else:
             param = [(k, v) for k, v in self.__dict__.items()
-                     if k not in ["name", "_op_use_c_code"]]
+                     if k not in ["name", "_op_use_c_code",
+                                  "output_types_preference"]]
             if param:
                 return "%s{%s}" % (self.__class__.__name__,
                                    ", ".join("%s=%s" % (k, v)