5. BagNode

Last page update: November 10, 2011

We discovered in the previous section that we can associate a set of attributes to each item, and we know that each item is a BagNode.

We remember you that a BagNode is a class composed by:

• a single label.
• A single value (or item).
• One or more attributes.

If you need to work with nodes, you may get them with the following methods:

• getNode(): return a node.
• getNodes(): return a list of nodes.
• getNodeByAttr(): return the node who has the passed couple “value-attribute”

>>> mybag = Bag({'paper':1,'scissors':2})
>>> papernode = mybag.getNode('paper')
>>> mybag.setItem('rock',3,color='grey')
>>> rocknode=mybag.getNodeByAttr('color','grey')
>>> nodes=mybag.getNodes()

The getNodes() method implements the Bag’s property nodes:

>>> mybag.getNodes() == mybag.nodes
True

If you have a node instance you may use one of the following methods:

• hasAttr(): check if a node has the given pair label-value in its attributes’ dictionary.
• setAttr(): receive one or more key-value couple, passed as a dict or as named parameters, and sets them as attributes of the node.
• getAttr(): return the value of an attribute. You have to specify the attribute’s label. If it doesn’t exist then it returns a default value.
• delAttr(): delete the attribute with the passed names.
• getLabel(): return the node’s label.
• setLabel(): sets the node’s label.
• getValue(): return the node’s value.
• setValue(): set the node’s value.

>>> print papernode.hasAttr('color')
False
>>> papernode.setAttr(color='white')
>>> print papernode.getAttr('color')
white
>>> papernode.replaceAttr(color='yellow')
>>> papernode.delAttr('color')
>>> papernode.setLabel('sheet')
>>> print papernode.getLabel()
sheet
>>> papernode.setValue(8)
>>> papernode.getValue()
8

For a complete list of the BagNode methods, check the BagNode section.