To handle lists in Dynamo you may want to choose the python editor. It’s a very strong tool but taking the non-typed nature of python it’s not that easy determining what kind of input data you have.
Even if IronPython is integrated in the .NET framework you cannot just test for IEnumerable interfaces as some sets are python native and do not share same inheritance.
To determine if an input data is a list you can use the following snippet:
t1 = t2 = False
if isinstance(unit, (tuple, set, list, dict)):
t1 = True
if hasattr(unit, '__iter__'):
iterstr = str(unit.__iter__())
if re.search('System.Array', iterstr):
t2 = True
return t1 or t2