class Node:
    COMMENT_NODE = 1
    PROCESSING_INSTRUCTION_NODE = 2
    TEXT_NODE = 3
    ATTRIBUTE_NODE = 4
    DOCUMENT_TYPE_NODE = 5
    NOTATION_NODE = 6
    ENTITY_NODE = 7
    ELEMENT_NODE = 8
    
    def __init__(self, nodeType, nodeName='', nodeValue=''):
        self.nodeType = nodeType
        self.nodeName = nodeName
        self.nodeValue = nodeValue
        self.childNodes = []

def _get_textContents(node):
    for child in node.childNodes:
        nodeType = child.nodeType
        if (nodeType == child.COMMENT_NODE or
            nodeType == child.PROCESSING_INSTRUCTION_NODE):
            continue
        if nodeType == child.TEXT_NODE:
            yield child.nodeValue
        elif (nodeType in [
            child.ATTRIBUTE_NODE,
            child.DOCUMENT_TYPE_NODE,
            child.NOTATION_NODE,
            child.ENTITY_NODE,
            ]):
            continue # or you might prefer, e.g, to look inside attributes
        else:
            # iterate through elements are left
            for text in _get_textContents(child):
                yield text
    
def main():
    top = Node(Node.ELEMENT_NODE, 'top')
    p1 = Node(Node.ELEMENT_NODE, 'p')
    p2 = Node(Node.ELEMENT_NODE, 'p')
    top.childNodes.append(p1)
    top.childNodes.append(p2)
    p1.childNodes.append(Node(Node.TEXT_NODE, '#text', 'foo'))
    strong = Node(Node.ELEMENT_NODE, 'strong')
    strong.childNodes.append(Node(Node.TEXT_NODE, '#text', 'bar'))
    p1.childNodes.append(strong)
    p1.childNodes.append(Node(Node.TEXT_NODE, '#text', 'baz'))

    p2.childNodes.append(Node(Node.TEXT_NODE, '#text', 'qux'))
    assert list(_get_textContents(top)) == ['foo', 'bar', 'baz', 'qux']
    assert ' '.join(_get_textContents(top)) == 'foo bar baz qux'

if __name__ == '__main__':
    main()