def __init__(self, key, item_type, default_value=None):
        """
        :param item_type: SessionVar defining the type of each item in the list.  The key attribute
        of item_type will be ignored - you can just pass in None
        """
        if isinstance(item_type, type):
            raise ValueError('item_type needs to be an instance of a SessionVar and not a class')

        super().__init__(key, default_value=default_value)
        
        self.item_type = item_type
def __init__ ( self , key , item_type , default_value = None ) : if isinstance ( item_type , type ) : raise ValueError ( 'item_type needs to be an instance of a SessionVar and not a class' ) super ( ) . __init__ ( key , default_value = default_value ) self . item_type = item_type
:param item_type: SessionVar defining the type of each item in the list.  The key attribute
        of item_type will be ignored - you can just pass in None