':param value_type: a column class indicating the types of the value'

def __init__(self, value_type, default=list, **kwargs):

    super(List, self).__init__((value_type,), default=default, **kwargs)
    self.value_col = self.types[0]
    self.db_type = 'list<{0}>'.format(self.value_col.db_type)
