'Returns a shallow copy of the AddExpression atom.
Parameters
args : list, optional
The arguments to reconstruct the atom. If args=None, use the
current args of the atom.
Returns
AddExpression atom'

def copy(self, args=None):

    if (args is None):
        args = self._arg_groups
    copy = type(self).__new__(type(self))
    copy.__init__(args)
    return copy
