diff --git a/lib/spack/spack/spec_list.py b/lib/spack/spack/spec_list.py index bc473f530cce11f22cc3b70e57af3eb99c138432..1aa0ab870e665d4b08d1dfffd2cc710b4fd4e699 100644 --- a/lib/spack/spack/spec_list.py +++ b/lib/spack/spack/spec_list.py @@ -25,7 +25,11 @@ def spec_ordering_key(s): class SpecList(object): - def __init__(self, name='specs', yaml_list=[], reference={}): + def __init__(self, name='specs', yaml_list=None, reference=None): + # Normalize input arguments + yaml_list = yaml_list or [] + reference = reference or {} + self.name = name self._reference = reference # TODO: Do we need defensive copy here?